Er... lots of ways to improve it. First of all, no go on AMD for budget gaming. Budget video encoding or 3d content creation sure, but not gaming. Second, I absolutely agree on the power supply. Raidmax = bad.
Here's a build. Lucky for you I like to make builds while watching SC2 streams. I used us.ncix.com since they have free shipping and it worked out well on a few (almost all) parts compared to newegg. Part picker is often out of date so I don't use them as a rule.
CPU - Intel i3-3220 ($110) An Ivy Bridge is going to be a far better gaming processor than Bulldozer, even though you can't overclock it. Super bonus points: cheaper too.
Mobo - MSI B75M Cheapo ($44) This + the lack of a heatsink is actually why the i3 system is significantly cheaper than the one you were planning on.
Video Card - EVGA 560 ($170) This is the big show piece of the build. It's significantly more powerful than what you were considering.
RAM - AMD 2x4gb 1600mhz ($30) I went with the 8gb for $15 more.
Case - Bit Fenix Merc Alpha ($40) It's a case. It's not crap, though it won't wow you. I have one, so I can vouch for that.
PSU - XFX 450w ($53) Much, much higher quality.
HDD - Seagate Barracuda ($54) Cheapo, but only 500gb at a time when 1TB is relatively cheap again.
DVD Burner ($17)
Total Cost: $530 at checkout, but $40 in rebates.
Actually, here I fail. I forgot about taxes. !! Well crap.
$530 + taxes = $572,
$530 after rebates... over budget!
To cut the cost further, drop the video card to a 7770 (midway between the 7750 you were looking at and the 560 above)
and cut the CPU from an i3-3220 to a Pentium 2120
That would bring you down to: $467 at checkout
roughly $505 after taxes.
But then you get $25 in rebates... eventually.
Hope that helps!
P.S. And as coachmark suggested, you can go for a used video card if you want. The marketplace here should probably have some 460s, maybe even a 560 at $100 or less.