Powercolor I've heard isn't that bad, and the quality can't really be less since the main chip and board is still built by ATI.
I did find on the back of one of my magazines, the cheapest 7800GT, going for about £180 and thats not bad really. You'll have to work that out in dollars
And yeah, the X850 would be alot better, but do note that with any ATI card under the 1900 range I believe, you don't get Shader Model 3 built in support. Yet, it'll be fine for games and Shader Model 3 built games will work on it, but you won't get the full range of effects used, but should be a fine upgrade.
6800GS:
Like I said though above, the Geforce 6800GS is also a good card, cheap and supports Shader Model 3.
Its one card now, below the 7800 in specs so not bad at all.
They can also be overclocked alot as well.
The line of 6800's was cancelled you see, and they released the 6800GS, to replace it which has slightly less pipelines than the 6800GT, but the speed of the card is infact faster than the GT, and with an overclock, can be just as good, and even better.
Though with this card and cards in this range, don't expect high resoloutions on the newest of games to run above 30fps on the best settings possible, though on lower resoloutions like 1152x864, and 1280x1024, expect in the 30's-40's-60's with high settings, which isn't bad for a card that costs about £150