Well, the HD 2900XT is an option.
Newegg.com - SAPPHIRE 100201SR Radeon HD 2900XT 512MB 512-bit GDDR3 PCI Express x16 HDCP VIVO Video Card - Retail
Performs very close the 8800GTS, does better in certain games, does worse in other games.
VR-Zone : Technology Beats - ATi Radeon 2000 Series Launch: X2900XT Review
That graph is a good one for you to look at as it compares all 3 (2900 and the 8800 320 and 640).As you can see the 640MB performs better in high resolutions/ heavy AA/AF. Also Neverwinter Nights doesn't run too well on the 2900 but in Oblivion it performs almost identical to the 8800's.
In Companies of Heroes it tears the 8800s up, makes you think about R600's true potential.