I dont see anything exciting coming until Q3-4.
ATi launched the HD3870X2 and nVIDIA will launch the GF9800GX2 and GF9800GTX. The former is G92X2(SLI on a stick and direct competitor to HD3870X2) while the latter is a G92 core with higher clocks(we dont really know a lot about this one).
If the 9800GTX retains the 256-Bit bus then i doubt the performance increase we can expect over the 8800 Ultra.
Personally i would wait for something a bit more groundbreaking, something that can give me the performance of 2 8800 GTXs without the hassle that is SLI or Crossfire.
Anyway if you dont game in high resolutions then you should consider getting the 8800GT 512MB or the HD3850 256/512MB