As of now I would honestly wait for the 560GTX's to go down to a price you like. They are probably the best mid-range cards out at this moment.
I run a 460GTX myself but it is the 2GB edition and benchmarks/over-clocks insanely well. And I got it for a very cheap price (it went through the till the wrong price - supposed to be £170 at the time and it only cost £120).
Now I would get a 560GTX - but as said I only recently got mine (about 8 months or so a go) and won't be upgrading any time soon.