Just no to Nvidia. Every Nvidia suggestion I've seen has been shit, each Nvidia card has a cheaper matching ATI card that can almost always be OC'd or unlocked.
For lower-end cards this is somewhat true, but you can't really make this generalization. NVIDIA makes higher quality cards at more conservative clocks with better cooling systems in the reference designs than AMD. If you are looking at the <$100 price range, there are more viable AMD cards, but above that point the NVIDIA cards are superior.