Also consider what future games you may want to play. Like others here I'd suggest nothing less than a 6850 or a GTX460 GPU as minimum. Personally, I'd take the 6850 over the GTX460. For CPU I'd say a minimum of a i5 2400. However if your budget is tight and you are forced to get a i3 2100 now at least get a mobo that can be upgraded to IB down the road. Then in a year or so you can replace the cpu for something better. I would give the same advice if going the i5 2400 route as well. Also make sure the power supply will handle future upgrades as well. 8Gb RAM is nice so if you can get it great but 4Gb will be perfectly fine for gaming so don't sweat it if you need to drop down to 4Gb RAM to save a few dollars.
Budget rigs are nice but you have to be careful you don't box yourself into a situation where you cannot upgrade things. Especially the GPU. If buying a built PC choose a company that has a custom configurator so you can choose the individual parts you want. Many online companies offer this feature.