According to Wikipedia, there was also a 6800 Ultra Extreme. Not sure if it was released though.
Please reference the top post in the thread. The Ultra Extreme was released but only in limited numbers, buyers were typically chosen by lottery. eVGA is the only card maker that I can confirm that made them. I read that Gainward was planning a 6800 Ultra that was even faster, (550 core, 1300 memory are supposed to be achievable) but that one was liquid cooled with a projected price of around 800 Euros. I don't know if any were released. $550 USD for the eVGA one was expensive enough, 800 Euros would have been an outrageous price that not many would have been willing or able to pay. I have also read rumors of a possible XFX Ultra Extreme, but never seen even a picture of one. The GPU's had to be hand picked and tested from the ordinary 6800 Ultras which is a time consuming and labor intensive process which is why these limited edition cards with super overclocks are so expensive.
It's funny, though, because every reference I see for the 6800 Ultra Extreme says they were released only in PCIe but I have yet to see a PCIe version, only AGP which nobody mentions.