Here are a few names that haven't been thrown into the mix, Mercenaries 2 and GTA IV. Both are good shooters and Mercs2 boasts true drop in/drop out co-op so either of you can go at it til the other wants to hop back in. I've seen GTA IV multi-player in a few videos and it at least seems like a good bit of fun.
Another thing, why not try a local store like Game Stop or Block Buster for the games? Ebay might be cheaper but it's easier to get ripped off that way
Seeing as how you mentioned SSX for Ps2 I'm going to recommend PURE because it's a beautiful looking racing game that supports multiplayer. Of course Cod4 and world at war for Fps. Street fighter 4 and soul calibur 4 for fighting game genres.