Well, after all the noise made for the uber expensive USD649-699 GTX280, time for ATI to showoff their impressive performance/price ratio products. As you may already know 4850 is retailing at USD199 while 4870 is only at USD299. Nvidia responded by lowering the price of 9800gtx to USD199 while pushing out the 55nm 9800gtx+ at USD229 next month.
A bunch of reviews just came out for 4870, so just check them out and make your own choice.

AnandTech
Ars Technica
Bjorn3D
Expreview
Hardware Canucks
Hot Hardware
PC Perspective
The Tech Report
TweakTown