LGA 775 is now dead so unless you are reusing an old board or an old processor you dont really want to go that route. You can go for an Intel i5 or an AMD Phenom II x4 for about the same price, which one is more appropriate depends on your budget and usage.
I definitely agree with hunter in going with an i5. I would not go for a 955/965 though. If you're willing to pay that much for a high end AMD, might as well splurge a tad more for an i5 IMO . If your budget is limited, definitely consider one of the cheaper phenoms/athlons (x2 550, x3 720, x4 620, depending on what you are using this pc for).
Off the bat though, I rather get a 4890 over a gtx 260 at that price range. I'd look into a spinpoint f3 over wd's caviar black. And as hunter said, no rosewill