Processor is important as well, so just in case - which processor are you looking at?
For graphics card, I'd say nVidia GTX560Ti or better. The Ti is what I use and it works perfectly for BS2 and A-10C with everything pretty much maxed and hacked high.lua for extra detail at long distances. If you want to have some extra margins, got either for a 2GB version of the 560Ti, or a 570. (Or even 580 if you have the money on hand.)
There is no less than three main versions of the 560 - the 560 without the "Ti" is weaker and cheaper, but should also be quite acceptable. Personally I don't feel it's perfect value, but that is of course up to your own budget. The 560Ti is the "standard" for 560's, very good value. There is also a version called the "GTX 560Ti 448", which uses the same silicon as the 580, but with some parts of the silicon disable, and is the strongest of the 560's.
For Radeons, I feel someone else might be better at offering advice, but in general something like a 6850 or better should do good.