Which PSU and RAM should I get?

[DataSnake]

I'm building a midrange gaming PC. Here are the parts I've picked so far:
Mobo: Biostar a770e3
CPU: Phenom II x4 945
Video: ZOTAC GeForce GTX 550 AMP! Edition
Case: Rosewill Challenger
Hard Drive: Seagate Barracuda 500Gb
DVD: Samsung SH-222ab
Other: WiFi b/g PCI card

I'm currently torn between a Rosewill Stallion rd500-2db and a Cooler Master eXtreme RS500. Which is better, or would neither work for my rig?
Also, I'm considering getting 2 4gb sticks of either Gskill's Ripjaws or Sniper DDR3/1333, but they aren't listed under "compatible RAM" on BioStar's website (though they were recommended by Newegg's memory finder). Will they work anyway, or should I play it safe and just get 4 2gb sticks?

 

[rvilkman]

The ripjaws should work just fine for you. There is a shell shocker deal coming today at newegg for 2x4GB 1333MHz ripjaws X so you should probably check that out.

I assume you are on a really tight budget to make the selections you are making. Could you actually list your budget so we can tell a little better what we are working with here?
Maybe there are other suggestions for better components we can make.

As for PSU: quality one from Antec, Corsair, Silverstone, Seasonic or XFX.
Don't skimp out on the PSU, it's the one component in your machine that if it fails it can take every other component with it.

XFX 450W $59.99 ( $44.99 after rebate )
XFX 550W $69.99 ( $49.99 after rebate ) very nice rebate on this one
Antec Earthwatts 500W $59.99

 

[DataSnake]

Budget: about $500 (I already have a 1280x1024 monitor, keyboard, extra copy of Windows 7, and an extra mouse and keyboard). I can't put up much more up front, so rebates aren't very useful to me. In case you were wondering, the RS500 was recommended in nVidia's "$600 crysis PC" feature, and one of the newegg reviews for the ZOTAC said it worked with a 500w Stallion, so that's where I got that.
Also, if it helps, I'm planning to use it for gaming, but also for programming, running a virtual Linux box, and Mathematica (hence the Phenom and 8gb RAM)

Thanks for the tip on the RAM, I was a bit worried b/c I read somewhere that it requires an AMD 790 and the mobo I'm getting only has a 770, but I thought I'd ask on the off chance; glad I did!

 

[DataSnake]

Looked at the brands you recommended, the Antec BP550 looks to be inmy price range.

 

[DataSnake]

Best answer selected by DataSnake.