Unless you're anal about power consumption, go with the 8800 Ultra. It's cheaper and does the job just as well on almost every game. Of course, if you're looking for super high end, you're better off getting the Geforce GTX 280. That's the best card on the market right now.
8800 Ultra is useless. Costs twice as much as a GT and gives you maybe 20% better performance (in addition to eating up considerably more power).
If you're going cheap, 8800GT is the way to go. Not sure if its the same where you are, but it runs about 120USD here compared to the 200USD+ of the 8800 Ultra.
In the 200USD+ range, the 9800 GX2 blows away the 8800 Ultra and is currently sitting at a sub-300USD price tag.
EDIT:
QUOTEisn't 9800 almost same as 8800?