As I'm contemplating setting up a new (virtual-tabletop) saga, I'm also thinking of how to set up a website to support it. I generally set up a website for my campaigns, and I think it's doubly important for an Ars Magica saga as a lot goes on outside of sessions.
My current D&D campaign follows the Shackled City ready-made campaign. I support it with a Yahoo Group that provides a mailing list to coordinate sessions and talk a bit between them, and by a wiki to supply background, house rules, character sheets, and session logs.
For an Ars Magica saga, I think a lot more is happening between sessions so a mailing list will not be satisfying. It is certainly workable (even just an email or a forum thread is workable), but not enough. The most promising idea I have come across yet is wetkipia, that provides a (free) wiki with inbuilt-forums and RSS. You get the ability to easily create "web-pages", to respond to comments by email, and to work within a forum to resolve OOC issues, seasonal developments and events, character advancement, and so on.
Something that's missing is active tables. I would like to be able to communally edit a "spreadsheet" just like a wiki allows me to edit a "document" - to be able to edit entries in cells and not just text. That would allow me, for example, to have a database of raw vis in use by the covenant, and have different players withdrawing it, sources adding to it, and so on. Yahoo Groups actually addresses this to some extent by providing tables, but they are not active.
So, these are my ideas. I'm open to others.