I was given the task by a friend to build a PC to play games like HL2, Black Mesa and Borderlands 2 with a budget of around $400. After reading up builds and benchmarks I came to the conclusion to go with an Intel i3 as they seem to have a lot of power behind them for a Dual core with four threads.
My location is Australia, so the price varies quite a bit as a pose to US pricing.
Here's the build I've got. I've already got the HDD/OS covered. http://pcpartpicker.com/p/1O8Bk
CPU - Intel i3 3240 $135
MOB - MSI B75MA-E33 B75 $59
RAM - 4G Single 1600 Patriot-S $44
GPU - 2G 7750 Gigabyte OC $94
PSU - ANTEC VP-450P PSU $57
DVD - MSI DH-20AS6 20x DVD $16
CASE - Thermaltake USB3.0 Commander MS-II $58
Total - $463 AUD
Tell me what you think, or what I can change, these parts and pricing are from MSY.com.au, due to them being t he only place in my area with good prices + pickup.
Try squeezing in two of those RAM modules into the budget, or plan to get a second one soon after. Otherwise it should be a good system for the money. I suppose there aren't many more reasonably well looking cases to choose from. ;) (I kid)
I agree with ragingh4vok; use the athlon 750k. its what im using right now and its a beast for the money. Do you absolutely need an optical drive? The Corsair CX500 is only 3 dollars more expensive (http://www.newegg.com/Product/Product.aspx?Item=N82E16817139028). I am also using it and its great.
For a low budget like that you might want to go with an AMD APU, the graphics on them arr not that bad, however you will want to get faster ram for an APU