I'm using the zalman vf700cu, and it cools really well. I dont care about exhausiting hot air, because I have case fans, you know? But it's really easy to install, and it works with a lot of cards. I've used it on my 9800p, now using it on a x800, and will probably use it on my next card as well. And Even when OC'd close to the limit, the temps are still better than stock cooling.
The Thermalright V1 looks like a good cooler too, but it's probably harder to install and wont fit as many cards. I guess the best way to find out is to try them all.