I'd recommend a quad core (check out the i5-2310 or 2320) to make sure that you can keep the pace with upcoming games and that your GPU doesn't get bottlenecked.
If you can wait, Ivy Bridge is coming out in like 2 months, and they'll bring the Sandy Bridge prices down. Maybe then you could afford a nice i5-2500k. If you have to buy the new build now, you're more futureproof and thus you end up wasting less money in the long run by getting a quad core rather than a dual core.
Dear lord in heaven change the PSU. Rosewills have a terrible failure rate. NEVER CHEAP OUT ON YOUR PSU! Just do not do it. It has to be the MOST important piece of hardware in your machine. If it fails it can take almost everything down with it.