This is gonna hit your top end range, but honestly, you are getting a lot of value with this over trying to cheap out too much on some parts.
I based this PC on the cheap but speedy i3 2120 3.3Ghz cpu that is really all you need for a budget gaming rig like this; you can look at configuring an AMD x4/x6 setup for a similar price that hits about the same speed, but Intel cpu's are just better at gaming over AMD cpu's, even when running AMD gpu's. I didn't pair any aftermarket cpu cooler since you don't need one on a budget box, plus the i3 or the H67 will not do overclocking.
I picked the MSi H67 microATX board for it being fairly cheap, decent and it comes with some nice features as in 4 DDR3 slots, three 1x pcie along with your 16x pcie for your graphics card. I threw in set of value set of 1333 ddr3 8gb set (2x4gb) that would work, but if you go with a faster cpu/mobo combo, you can spend $5-10 more for the 1600 speed if you want.
You can go a bit cheaper with a lower end microATX board that only has 2 dim slots, but you are limiting your expansion. However, you can take a gander at cheap ECS and Biostar boards since some of their ATX p67/z68 boards have been as low as $30 when on sale. They don't match the quality of the bigger names like Gigabyte, MSi, Asus or Asrock, but they are OEM supplies and if you don't plan on overclocking, they will work just fine for cheap builds such as these. Just due note that I paired this setup with a microATX case, but you can easily upgrade this if you wish.
I threw in a 2TB 7200 drive that eats up about 1/5 of your budget only because it hits a very good price/GB ratio over the 1TB or smaller drives. The bigger drives are just cheaper now and means good things since we are getting close to pre-flood prices again. If you do want to save a few bucks here, you can grab a 1TB drive for about $20-30 cheaper, but you'll loose a bit of value; honestly for your build, 20-30 won't kill your wallet specially when we are talking about doubling your storage capacity. Also, stick with 7200 drives as your boot drive.
As for graphics? I'd suggest the AMD 6850 or the 6870 for around the $130-150 price point. There's so many options here, but the 6850 I configured is a great value. You can look at the lower 6770 or 6750 that will play madden 08 just fine, shit you can even look at the nvidia 550 ti for $100ish.
I picked the XFX 450w 80+ bronze power supply as its on sale for $30 right now and all you really need for power. Even with your setup, you'd probably only use about 200-225w on load, if that. You can look at other brands like Antec, Corsair, Cooler Master, OCZ and such in this price range that are around the 400-600w range and have 80+ certifications. But sales will come and go and I could easily recommend a different PSU tomorrow if something else pops up on sale. The Corsair 430w v2 builder series is a popular choice that I usually recommend since its normally around $20-30, but right now its not. Actually it was $17AR not too long ago, but again, you go with the sales.
All of this is housed in the cheap, but nice Fractal Design core 1000 mircoATX case. For $40, its a great value, but if you were looking for more expansions in the case, then look at the NZXT source 210 or 220; personally I like the looks an features of the 220 for $45ish since it comes with USB 3.0 front mount (mobo I picked does not have 3.0, fyi) and has a lot of cooling options as well as hard drive expansions. But again, so many on the market to choose from; I just picked one.