So I've been looking at cards like the Radeon 4870 and Nvidia 250, but haven't really settled on anything yet.
What card(s) do you guys think will bring the most improvement to the system for gaming (Dragon Age, L4D, Mass Effect...) for <$200?
Also, I am considering doubling up on RAM - worthwhile?
^good choice. I would have to admit that this card is the best bang for your buck at under $200. There is the 5770 that offers DX11 support, however, my fear is that even with DX11 support it may struggle with DX11 games. I think the safest bet is the 4890 what will give you a huge boost in power over your current card. The XFX card you picked out has a nice cooler and MIR. It's a good price.