Okay, if you're talking buying out of a box, I suggest a laptop. Seriously. If you're not getting a laptop, then you should build it yourself and save a TON of cash. Cash you can use to get kickass games.
My laptop is 3 years old, and it can run Crysis on Medium without hitch. It can go to very high, but starts juttering hard when combat gets heavy. Runs well on high, until it starts frying my legs after 20 minutes or so, then it starts slugging because it's overheating.
Honestly, though, a good laptop can do everything you need it to out of the box, but a great desktop should be hand crafted so that not only does it kick much ass, but also have that emotion attachment of I BUILT THIS DAMN THING NOW WORK DAMMMIT!!!!!!!