May I suggest this 6950
It's an XFX 6950 2GB for $190 after a $30 mail in rebate (deal ends 5/8). Also XFX has a lifetime warranty which is really nice.
This model has 2 mini display ports where as the other model has 1 regular display port. The perk with 2 is that the card can support 4 monitors!
A personal reason I like AMD HD cards over GeForce is the multi-monitor support on a single card. The 6950 is an especially good entry model for this since it has 2GB of video ram. Some games don't support the multi-screen option (called Eyefinity) due to what I can only assume is competitive reasons (SC2 for example).
I'm no expert and still in the process of looking at options for my own gaming PC, so I can't speak from experience to say if the multi-screen set up is nearly as cool as it is in my mind. For what it's worth I posted this
just earlier today concerning multi-screen options.
From Tom's GPU hierarchy charts it seems that the 6950 and 560 Ti are at least on the same tier (6870 is one below).