My tip is wait another year or so.
Building a pc for the next gen games now is way too early and way too expensive.
ANother tip is find a good site with a good barebones system you can piece together yourself. It may cost a few bucks more, but most of those places put together the main componenets for you (mainboard, cpu/heatsink w/thermal paste, etc.) as well as doing a test on your components and a burn-in period. Nothing is more frustrating than building a new pc, flipping that power switch, and nothing happens cuz' you happened to get a faulty piece of hardware.
I got my last barebones at
Monarch COmputer Systems as well as two of my buddies. They may not be the cheapest compared to newegg or someplace like that, but you at least know what you are gettting is going to work, as well as excellent customer support in the future.
ALso another big tip is dont skimp on your power supply. It's easy to get a new tower and see that it comes with a 500wt power supply and think you're good. FIND OUT what kind of power supply it actually comes with and look it up online for reviews, comments, etc. I fried a power regulator chip on my mobo and had to RMA it due to a crappy generic power supply that came with my tower. It conked out on me and just before it stopped it must have surged or something, frying my mobo's chip in an instant. THAT was a good smell let me tell you.
Anyways... a Power Supply in my opinion is the most overlooked piece hardware in any system. People are too interested in what vid card, cpu, and whatnot that they tend to skimp on the PS and don't realize how important it really is nor how much damage it can do to your system if it's crappy.