I think TigerDirect is pretty good, but I've always used the Egg. I'd say stick with it if you live in the US, the shipping is unbeatable and their customer service is incredible!
That ATi card is pretty good, but I don't know much about them. I'm an Nvidia guy. Personally, if you were willing to branch out, I'd get a 7800GT for just a few more bucks. That'll really make your system fly.
I think they're about 300 bucks right now. Worth every penny.
But, you said you wanted to stick with ATi. I do believe that's a great video card, though! Wait for some expert opinions, though.