Someone, yes. But what happens when that magus is not there? What happens if you're in a foreign aura, where every fatiguing spontaneous spell risks the chance of botch? ArM5 p.81 states that a formulaic spell cast in a quiet situation uses a simple die, but no such statement is made for spontaneous spells...
That's why I included those spells. IMHO, every magus should learn them in their early years.
I can't post what 10 indespensible spells are, because I think it varies with the magi and magae who will be part of it. Indeed, if we're designing a covenant from scratch, I pick spells for the Grimoire based on what my sodales spells are or might look like.
I can, personally, as my magus, spont the sense of magical power without fatiguing. But I do agree you'd want to learn formulaic spells for them eventually.
Couple of points... is your magus on every adventure where it might be needed?
That will change in an infernal and divine aura, when you have to contend to the reductions in casting score due to realm interaction.
Hi,
I'd suggest that Aegis is much less important than advertised for a Spring covenant. First, it costs vis. Second, a level 25 aegis is not big enough to keep out anything interesting, and the magi might not even penetrate. (But is does represent a stress roll with 5 extra botch dice every year...) Since Ars Magica is a quasi-storytelling game, an Aegis is never large enough to keep out anything that satisfies the story, "something is getting through your Aegis and doing annoying things." I'm not saying don't have one, but I think it's very saga dependent.
That's my basic 10. Next...
Anyway,
Ken
I've seen it brought up that an Aegis isn't important because magi can deal with the problems. Of course, they can. And I'll submit the Aegis is important for the covenfolk, primarily, and it keeps the anklebiters away from the covenant so that the magi can spend their time concentrating on their important work, rather than deal with the constant interruptions from low might creatures getting into a covenant. An Aegis20 is pretty easy to cast and learn, and getting a couple of people to commune on it makes it easy. Give it to the Cautious Sorcerer to learn, invest some time into mastering it, and it becomes very easy to cast reilably. And many people believe that one level of mastery mitigates the risk of all botch (I'm not one of them) that was heavily debated in this thread.
And if you're moving a grog (rather than instantaneous translocation) you don't need requisites, the other items get moved as a consequence of the body under or holding the items moving. But if it's a teleport spell, yes, requisites are important, but these are casting requisites, and have no bearing on whether the spell can be learned, or even if it should be in the list... 
Hmm. What you need is very saga dependent. Absolutely. But not having an Aegis is actually inviting the storyguide to send minor faeries and demons to annoy you all year long. Also, why don't you apply the same caveat to combat spells? Whether you'll need them or not is saga dependent. Actually, I'd say that a combat spell is less useful than an Aegis, because you can substitute grogs for pila of fire, but not for an Aegis.
The point about botch dice is painfully true, if you assume that Rituals always inflict magnitude+1 botch dice. I assume, however, that since virtually every covenant has an Aegis, there are some very, very good books on mastery of the Aegis widely available; possibly teaching the Adaptive Casting mastery and Learn from mistakes mastery from HoH:TL. In my saga, the standard book on the Aegis is Notatus' famous "The shield of the covenant", a L3Q15 summa on mastery of the level 20 Aegis, with enough information to learn Adaptive Casting, that is as widely circulated as the Roots of the Arts and brings a magus to a mastery score of 3 with two seasons of study.
Most magi who read it take "avoiding botches" as a specialty, which reduces botch dice to (4+1)-(3+1)=1.
I almost missed this:
Hmm, I'm not too convinced about that. I can see you countering "well, if I create a magical thunderstorm, would the ground dry up as soon as the thunderstorm was over?". But still, I'm not entirely convinced, unless there's a reference I'm missing.
MP3Gain could help you to have the volume level between podcasts (89db)? or did you mean internal to the podcast? Within the podcast: get a multidirectional microphone and sit around it. AFAICT, your volume may be dipping because you are turning to face the other guys on at the table.
(Sorry I didn't reply. The only thing worse than the entire family being ill is both parents being ill while the newly recovered toddler is filled with joie de vivre and is tearing the house apart.)
Hence why I said eventually. They aren't vital straight away, but will be needed within 5 seasons of founding, IMO.
Oddly enough, in our saga, the odds are he will be, early on. He's local.
Rather than posting about spells that I think folks might reconsider to be important I'm going to make a case for why two of the spells in the top ten shouldn't be bothered with.
Chirurgeons Healing Touch heals a light wound. It does not do anything to any other sort of a wound (medium, incapacitating, and so on). Gentle Caress of Asclepus from HoH: Socitates makes a wound better by one level (i.e. light wounds healed heavy wound becomes moderate). I realize that Gentle Caress of Asclepus is level 30 but I just don't see a good reason to have Chirugeon's Healing Touch if it can only help the lightly wounded.
Wizard's Communion was used in previous editions of the game to be able to cast a spell from a text that was too difficult for anyone present to cast. In fifth edition, casting from texts isn't a big thing. Also when you use a casting tablet in general it is much easier to get a spell off. Wizards boost, in fifth edition, is a very cumbersome penetration booster (I'd have to double check to be certain that it even works with casting tablets). It could make a cool story to get your magi together and do wizard's communion in order to get the penetration you need for a monster spell but this coolness is ameliorated by a few factors:
The per magus penetration boost that wizard's communion gives you becomes smaller with each additional magus in the communion while the chances for botch become larger,
collecting arcane and sympathetic connections is most frequently an even cooler story, and
magic resistances in fifth edition, while stronger than in any previous edition are still in general too low to be insurmountable.
I suspect it's a level issue. We commonly have a magus who can pull off a level 5 InVi spell in an aura (with ceremonial casting to begin with) with at divide-by-5 spont. And if you're in the wrong aura, you bring it home first. Thus it doesn't depend so much on who can do it and where you are. Finding the Vis in the first place is far more important when you're in bad situations.
Chris
It seems I took a fairly different path when answering this. I thought about covenant spells: spells that are useful IN the covenant, not spells for doing stuff somewhere else.
Here is my list. I compuiled it when away from my books, so it is sketchy.
Cheers,
Xavi
Actually, as I said, I think the issue is that a lot of people assumed the question different from what it was.
The intent of the question was "which magical effects are so indispensable that someone at the covenant must be able to produce them somehow, whether by spontaneous magic, through a formulaic spell, with a casting tablet or with a magical item?" If a magical effect is truly indispensable, it's supposed to be on the list, even if it's a level 1 effect that you need only produce in a friendly aura with all the time in the world.
Many people instead assumed the question to be "what spells must be in the covenant's library" or "what spells must be either in the covenant's library or in some magus' formulaic or ritual repertoire"? Thus they left out effects that they did think indispensable, but that they judged could be produced spontaneously whenever needed.
As we say in the podcast, the spell was chosen but NOT ONE person who listed it wanted the spell as listed: we listed all requests for variants of spells by the rulebook version ( I think we say this in the podcast). So if you listen to number 13 again I think you will agree we did stress exactly this - no one would actually take Chirurgeon's Healing Touch as written, ever 
cj x
My own list consisted of:
Aegis of the Hearth
Aura of Rightful Authority
Fist of Shattering
Gather the Essence of the Beast
Lamp without Flame
Posing the Silent Question
Purification of the Festering Wounds
The Inexorable Search
Veil of Invisibility
Whispers through the Black Gate
Still, CJ and Darkwing made some good points about the various spells in their countdown. I really want to see the Top 30 now too!
Agreed. Fully. And I included as much in my answer to cj. Like all of us.
I put in Wizard's Communion as a conditional:
If the Aegis must penetrate, bring the Wizard's Communion. Especially because you will want penetration against everyone and everything, so ACs are not an option. If the Aegis does not need to penetrate, forget about the Wizard's Communion.
OK, here goes: saves folks having to listen to the podcast (unless they want to hear our discussion of the top twenty spells, which might interest some folks?). The top twenty contained only one tie, and that was easy to resolve because a similar spell of slightly lower level was mentioned by several people. The top forty led to three more ties, including a six way tie at 34-- I resolved it by putting spells voted for by authors for ArM5 ahead, and then by doing it by number of publications at current moment. A biased method, but as good as any. The one resulting tie I flipped a coin for! The resulting complete Top 40 Spells were as follows...
I see what you're saying, but I'm not really sure that actually produces the desired results any better. For example, I could say something to detect Vis is far more important that identifying its amount/type. The latter ones only matter if you're aware of its presence, after all. And if you can do the former, you can probably handle the latter two spontaneously. So should all three make the top list or only the one to detect the Vis. If you do that with just a few things you may just end up with a list that says you need to work with Vis and have a little protection, or something like that. At what point does a top-ten list become useless because of necessitated redundancy within it is then my question.
Chris
Yes, in canon Aegis of the Hearth must penetrate to prevent beings from entering.
Chris