Well, let's see. I'll compare the BFG 8800GTX ($360 at newegg now) with the BFG 9800GTX ($330).
Advantages for the 8800GTX: better fps at high resolutions in single-card setup.
Advantages for the 9800GTX: $30 less, no mailing rebate junk, consumes less, less heat, support for Triple-SLI (assuming you have a 780i board and a serious PSU and case).
For a single-card setup, and a resolution of 1680x1050 or more, I would still buy the 8800GTX, I think, or maybe the 8800GTS G92 512MB. It depends on the budget.
For 2-card setups, I'd pick the 8800GTS G92 512MB.
For 3-card setups, the 9800GTX.
Edit: you should probably compare the 9800GTX with the 8800GTS G92 first. If you don't need 3 video cards, you can stick with the 8800GTS G92 and save lots while still getting the same performance or very close.