Looking for suggestions for my new rig

Well, I've finally upgraded from a 6600gt and P4 Northwood to an HD4850 OC and E5200 at 3.7ghz. I'm itching to play some games I have seen mentioned over the last few years, but couldn't run. I'm okay playing some dated games since they are dirt cheap and I haven't received my government issued $23,452,432 stimulus check yet. Maybe I should change my last name to Bank.

Mainly looking for a FPS right now. I have HL2 with Esp1, but play the crap out of Counter Strike Source. I love the real guns of CS:S (Go GG-DM aka Pvt Bovine) and the tactical theme. So that might be the direction I want to go but staying away from WW2 shooters. Is there any out with decent online play or better yet, co-op modes? Some titles I could use some feedback on are any of the Tom Clancy lines, Battle Front series, CoD4. Something along those lines I guess. Not a big fan of the zombie games or else I'd already have L4D and Fallout 3 is on my list, but need to wait for the price to drop a bit. I checked 3 different CC's, but they were all out.

Side note, is Assassin's creed worth playing? I don't really like 3rd person games, but it came free with my CPU.

Thanks for taking the time to respond,
Skora

I decided to hold off on Crysis till the Max edition comes out if its reasonably priced. CoD4 looks more like a rail game and I'd rather go sandbox this time round. Do you know if there's any place that trades or gives credit for PC games? That's what I was hoping I could do with the Assassin's creed. Might consider it for World In Conflict too. That's taking me a little bit to get into and its not going well.

Thanks Mega, I started looking at the Tom Clancy lines and was interested in Vegas 2 since it has a coop mode or so says Steam. I'll look at Ghost Recon also. I just set up a trade of Assassin's Creed for Enemy Territory Quake Wars. I'll see how that goes.