On monday my new computer will arrive for me to build and as its a Q6600 quad core, 4Gb RAM with twin Radeon HD 3870XTs i want to find a game to test it out on which is also really good!
 
I currently have Crysis and CoD4 lined up to play on it, however i have already completed these (albeit on low graphics settings!) on my current system.  
 
So i am looking for system crunching, visually stunning games! The Witcher is currently the only one on my list as its meant to be a pretty good game (gamespot gave it 8.5) and apparently looks quite good too (the scenery and settings).
 
Anyone got any suggestions on other games i should get and try out?
 
Edit: Oh, and i have UT3 to try as well.

 
Two words: Orange Box.
 
World in Conflict is also excellent, whether you're an RTS guy or not.

Oh, i think my bro has the world in conflict!
 
Also, i might try and borrow the orange box off someone as i was never really keen on the half life games, dont know why! I generally prefer fighting other humans (i know crysis has aliens in..but its primarily humans).

i don't like shooting aliens too, but i ordered the orange box today (yesterday when i see the clock)
i like fps games, and i think you have to try everygame a bit... i played fair, but when i played it out, exually it isn't a good story at all. just like bio shock, to many bugs, but played it out. now with patch 1.1 it should be better, but don't feel to play it again. so orange box, 5 games for less than 5 bucks
 
i think you'll amusing yourself with the halflife games. it' s 24 hours playing only the 3 parts i guess

world in conflict is very cpu intensive my system gets to 12 fps when someone decides to triple nuke in net play

Seconded.

You do fight humans (or at least Combine humanoids) in Half-Life. It's not just aliens.
Also, let's not forget that the Orange Box includes the best multiplayer game of the year (if not the best ever), not to mention one of the most innovative games of the year.
Trust me, this is one box you're gonna want to have. It's that good.

I would also recommend the orange box because it has excellent games, but they really aren't that visually stunning. If you're looking for the latest and greatest graphics to test your system they won't be found in what are basically HL2 mods. Although TF2 certainly had one of the best art teams I've seen in a long time I could easily run it on max settings with just 2 gigs of ram, 1 3870 and an e6850. Same goes for Portal. Don't get me wrong, TF2 is one of the most fun multiplayer FPS games ever, I just want you to know what you're getting into.  
 
As others have said WOC has great visuals. WOC, Crysis, and COD4 are definately the most visually impressive games of 2007. You might also want to check out Gears of War. That's all I can think of for now.

for visuals alone, the OP already has the greatest games

I'd add another second to the list of Crysis, followed by World in Conflict and Call of Duty 4, in roughly that order. Unreal Tournament III might come in fourth place.
 
I'd also get The Orange Box purely for the value and gameplay; the visuals aren't card-crunching, but they DEFINITELY have a lot of effort put into making them look great. Plus, I can't help but love Portal.

Don't forget that the set includes Portal. You've technically not touched TOB until you've gone through that.

i'm exciting to get that box out of the store, at the end of my exams!
portal is a nice turn in the gameworld. you already had to think a lot in halflife (pussling) put now, you have breinbrakers in portal! I hope it isn't a big dissepointment!
 

If you want to try out the concept, some fans made a flash version of it: it lacks the same atmosphere and humor, but even though the levels are 2D, it gets the gameplay pretty dead-on. (note: the flash version was actually put online before The Orange Box was released)

thanks i'll check it

Meh, the flash version is a fun little distraction, but I wouldn't call it a good concept demo.  

Gears of War is def worth a try.
 
i also have to suggest Battlefield 2142, still looking stunning and great gameplay

Gears of War on PC? I thought it was 360 only! If i can get it thats definately on my list.

It still amazes me that the game was SERIOUS. When I first heard about it, I'd thought that it was actually a joke.
 

Has been out for like half a year; it remained "exclusive" to the Xbox 360 for only about a year or so.

I personally like the visual effect of Bioshock (despite the unpopular policy that you can only install the game X number of times). I had much improvement after upgraded my GPU too 8800GT and I can only imagine what your system can do.  So you may wish to test out the graphics of that game as well?  

Bioshock was never fully on my list as i am borrowing most of the games im testing off mates and my brother, and thanks to bioshocks unusual security method that might make it more difficult! Ill check ebay and amazon though, see if i can pick it up cheaply!

? didn't know you could play bioshock only a few times? how come? when you unistall it, you never can play it again? or what do you mean with that unusual security? i played the game on my 8600Gt bad card for that game, last level sucked

Yeah, the copy protection with bioshock is weird. When you install, you create an online account with your cd key, this then gives you 2 or 3 'credits' which are used whenever you install the game. Then, upon uninstall, you get a credit back again. This means that a cd key can only be used to install the game on 2 or 3 machines so stops people downloading it, but still allows the owner to uninstall it and reinstall it on a new computer etc. (This catches some people out as if you format your computer or re-ghost it you must uninstall it first otherwise you lose your credit!)
 
In theory its a good system, but server errors and people not uninstalling it properly make is buggy!