nVidia's 7800GTX 512MiB is currently selling for $749.

ATI's X1800XT 512MiB is currently selling for $699.

nVidia's card rules the roost, according to most benchmarks, and has better overclocking potential.  However, you can't find them anywhere.  ATI's card, although a slightly less capable product, can be had for as low as $640, according to some sources.  So, the question is, which would you get, if you were in the market for a high-end card?

Tell us, in the forums!