First Time build - Budget Gaming PC

This will be my first build. I'm upgrading from an Athlon 3200, 2Gb RAM, 256Mb AGP graphics card, lol.

APPROXIMATE PURCHASE DATE: Within the next 2-3 weeks
BUDGET RANGE: $400-500 Before Rebates

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Gaming (WoW + some newer games), Internet

PARTS NOT REQUIRED: Keyboard, mouse, monitor, speakers, OS (Win 7 Home Premium 64bit)
[see below for PSU, HardDrive and Case that I already have]

CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail
http://www.newegg.com/Product/Prod [...] sair%20750

Western Digital Caviar Blue WD6400AAKS 640GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive
http://www.newegg.com/Product/Prod [...] WD6400AAKS

Antec Three Hundred Illusion Black Steel ATX Mid Tower Computer Case - Retail
http://www.newegg.com/Product/Prod [...] 20illusion

PREFERRED WEBSITE(S) FOR PARTS: newegg.com

OVERCLOCKING: Maybe
SLI OR CROSSFIRE: Yes (but not right away)

MONITOR RESOLUTION: Current 1440x900 (but upgrading in next 3-4 months)

My rough build proposal:

AMD Phenom II X3 720 2.8GHz 3 x 512KB L2 Cache 6MB L3 Cache Socket AM3 95W Triple-Core Black Processor - Retail
http://www.newegg.com/Product/Prod [...] 6819103649

ASUS M4A79XTD EVO AM3 AMD 790X ATX AMD Motherboard - Retail
http://www.newegg.com/Product/Prod [...] 6813131402

G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL8D-4GBRM - Retail
http://www.newegg.com/Product/Prod [...] 6820231278

SAPPHIRE 100283L Radeon HD 5770 (Juniper XT) 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Prod [...] 6814102858

Sony Optiarc Black 24X DVD+R 8X DVD+RW 12X DVD+R DL 24X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA DVD/CD Rewritable Drive - OEM
http://www.newegg.com/Product/Prod [...] 6827118030

That comes to $482.96 (+$30 mail in rebate)

I think all of this goes together, but this is new to me, so any advice would really be appreciated. I want to build a system optimized for performance at my price range, so if I need to start from scratch, please let me know.

Thanks in advance!

^+1...
You get tighter timings for less...
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL8D-4GBRM
http://www.newegg.com/Product/Prod [...] 6820231278

And the HD 5770 is a very good option as it would offer similar performance as that of the 4870 and is next gen...
http://www.newegg.com/Product/Prod [...] 6814102858

So later on when you upgrade your monitor, add one more in crossfire later...

And you must have checked out the combos right?
http://www.newegg.com/Product/Comb [...] mbo.273353

If you are getting the X3 720, might as well get a CPU cooler right away...
Sunbeam CCTF
http://www.newegg.com/Product/Prod [...] 6835207004

Thanks for the responses so far! Updated RAM to the Ripjaws version referenced above. New total is $477.96.

I had considered the 5770 but have read mixed reviews in the forums as well as buyer reviews. I've read several that indicated the 4870 performs better than the 5770. Can anyone elaborate on this?

Here's the 5770 I was looking at:

SAPPHIRE 100283L Radeon HD 5770 (Juniper XT) 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail (same as the one gkay09 recommended above)
http://www.newegg.com/Product/Prod [...] 6814102858

I like the fact that it has HDMI and only requires 1 PCIe power connector.

As far as the CPU cooler, I figured I would upgrade when I'm ready to OC.

Thanks again for the feedback!

Thanks for the link on the reviews. I'll read up on it some more.

I also am considering either a 4870 or 5770 but I think id go with the 5770. for a couple fps less in some games i get dx11, lower power consumption and eyefinity. Plus when i need to upgrade i could xfire with another 5770 and put the hurt on alot of more expensive cards

^ For gaming that X3 is a very good option...And that mobo offers enough options for a good overclock...
The next best CPU option will set you back by ~$60 - X4 955
The only thing missing here is the CPU cooler...Even though you will not be overclocking at the beginning itself, I would suggest you get the cooler now itself as later on when you want to overclock, you wouldn't have to remove and replace the HSF and the after market CPU coolers have very good cooling performance even at stock speeds...So your CPU will run cooler...