Hmm... Tough decision...
1. Arcana Evolved
2. Lords of Madness
3. Wilderlands of High Fantasy (Hurry up, FLGS!)
4. Ebberon Campaign Sourcebook
Which is, in fact, the core of my current, and perhaps last, campaign. I've been using the Judge's Guild material for a long time now. Mostly its just been for the maps. I'm looking forward to the NG product, and have been for some time now.
Looking at non-d20
1. Aeon
2. Aberrant
3. Adventure
4. Ars Magica
And that covers just about any type of game that I'm looking for.