Of course the main book and players guide as well. And then any other book that might have merits/flaws you want. I'll even consider web-based stuff if its well-thought out as well, but I get final approval on that and No is No.
Mage would of course be the main mage book as well, and the players guide and then whatever type of mage you want to be.
And if someone can get their hands on the Combat book, we'll use that too. But only if we have it on the day of the first session so we can start with it. I don't want to introduce it to into the game part-way through.