I'd advise waiting til the end of month, if possible, to purchase your CPU. Intel's supposed to drastically drop the q6600's prices, as well as other processors, making the e6600 cheaper or the quad-core version viable.
Most comparable motherboards won't really change things much -- we'd be talking minor points on a synthetic at best. I'd suggest sticking within the range of the
Biostar TForce p965 to the
ABIT AB9, and keep an eye out for any features
you are interested in, such as extra IDE compatibility (to keep your existing drives) or preferred audio. I happen to like the MSI p965 and EVGA 650i simply because I've had luck with them so far. Don't go lower in price or your risk running into motherboards with less than reliable parts, or no real overclocking potential, and most higher priced boards aren't worth the costs at this budget.
There are some very good Open Box options available if you already have the cables, and don't mind a missing backplate and using online manuals.
RAM is cheap, and while you can spend a lot of time comparing them, this is really a matter of how much you're willing to spend. I don't see enough difference to justify going much past 2GB for ~110 USD, outside of a Vista environment where more is viable.
For video cards, it really depends. If you've got the money in your budget, an
8800 with a lotta RAM can probably last you a long, long time. That's probably only going to work if you keep your old drives, though, or are willing to stretch your budget. You can get a 7900GS for half that, and it'll play most modern games well at high standards, although I doubt it's Bioshock and Crysis- proof.
For PSUs, there are some pretty good
500 watters out there. It won't power a 8800GTX, or an SLI configuration, but you won't be getting to those on your budget <i>anyway</i>. Unless you've got a lot of spare drives, this guy seems to work fine for me. I don't see the point in spending an extra 40-50 USD for the extra wattage and interfaces that the Mid-Range build used unless you seriously plan to run SLI, which isn't viable on the p965 base.
For cases, I'd advise either the RaidMax X1 or (if you use the front-side ports a lot and prefer not seeing the insides of your computer) the CoolerMaster Centurion 5, both of which can be gained for 40-50 USD and work wonderfully. The Antec p180 is very, very quiet, refined, and easy to work with, hence the popular reviews... but it's also expensive, and for most people the results aren't enough to justify the cost.
Toss in an Artic Cooling Freezer 7 or a Zalman, depending on case.