Mr. Gency said:
Rainbow Six: Vegas and Splinter Cell: Conviction are the only games I can think of that I would recommend.
IDK about the first Rainbow Six, but Vegas 2 was a huge blast to play with my dad on Terrorist Hunt.
Also, I've had a lot of fun playing CoD splitscreen with friends recently. All of the recent good ones, we did Old-school mode in Cod4, Spec-ops in MW2 (and playing Nuketown with 7 easy bots on the other team and the kill-streaks set up for 10+kills).
But if you can't find a good console game, if you've got more than one PC, you can LAN some RTS games for a lot of fun, too. A friend bought LoRT: Battle For Middle Earth, and although we had to find some more CD keys online, we have great time playing together.
Basically, there are games still out there, you've just got to know where to look.