The 5770 is a good choice though your budget could get you a 460GTX for a bit more
Not a big fan of the GTX470 honestly. They run hot unless you get one with a very nice aftermarket cooler, like the Gigabyte one with dual fans. Had a guy bring one back because the stock fan wouldn't keep it cooler than 100c under load. And it wasn't the only one.
I say 5770. Then pump up to 4GB of RAM.