From a surround sound perspective, I've been pretty impressed with Assassin's Creed 2.  Some pretty spooky effects, and great placement of sounds in relation to your character/camera.  Found some secrets specifically thanks to my surround speakers.

I think any of these games that allow you to roam freely or complete a mission show good use of surround sound.  It helps you lose yourself in the game.  I couldn't imagine playing these games without the surround sound.

I haven't got my 4t system yet but I am looking forward to some gaming when it shows up. (yay for the holiday wire kit promo to help push me over the edge!) I use an HTPC but it can game well and will even better with the new ATI 5750. I'll now have true audio passthrough for my Blu-rays. I have a 25' HDMI cable from my main gaming PC to the TV that will go to the Onkyo as well. I'm sure I'll end up playing even more games in the living room now.

I can say that Dead Space, FEAR 1 and 2 had good sound and that Left4Dead 2 has even better sound envelopment than the first version.I play it on some logitech z-5500's currently and the 5.1 is brilliant. Hearing my games on the Aperion's will be a nice update. I'll hit this forum back up once they arrive, I have quite a few games to try out and will do so.

..I may have to warn the neighbors though, just so they're not too freaked out at the sounds of screaming zombies and chainsaws. heheh

 

Just finished the single player campaign for COD Modern Warfare 2 this past week, and that game has an awesome soundtrack.  Guns, RPG's, choppers, etc. Really makes you feel like you are in the middle of WW3.

Its also worth mentioning Gears of War 2 in this discussion.  By far, it takes advantage of my subwoofer more than any other game I own, and all the weapons/explosions punch very hard...

Since no one has mentioned it yet, I'll give a shot out for Uncharted 2.  Lots of surround activity and deep bass in certain scenes.  It's also the only PS3 game I have that gives me the option to provide LPCM to my receiver to get uncompressed audio- and it's encoded in 7.1 too.  Sweet!  The game is fun too (both the main story and the multi-player online), so my Aperions have been eating it up.