for just under the $150 price point you can get a GTX 460 768
for 1 gb cards the GTX 460 and the Radeon HD 6850 are both excellent cards and can handle pretty much anything you throw at them. They sell for just under $200 these days but you can almost always find them for around $160- $180 ( and occasionally for $150 ) after rebate at places like NewEgg or Tiger Direct ( though TD has an iffy rep for rebates )
Chances are if youre considering a graphics upgrade you will also need a power supply upgrade as most of these card will need a minimum of 500 watts psu to run smoothly. Keep that in mind when you shop.
Actually, that's what I ended up going with. A EVGA GeForce GTX460 1G card. Found it on Amazon for $160 (not including the $20 rebate). With the free shipping from Amazon, that gives me a net price of $140. Given that the 5770 was going for $145, I figured the upgrade was worth the other $15 even if I didn't get the rebate.
Power supply shouldn't be a problem...mine is 600W.
Thanks for the help guys!