I don't understand it. I was thinking about going SLI but im not going to, unless the 8800 640mb gts goes down to 150$ or below. For some reason in some, if not most, cases the 8800 640mb gts costs more than the 8800GT and almost as much as the 8800gts g92, WTF. I know people are dumb and still think that the new 8800 gts is the same video card as the old 8800 gts; so they buy the old one by mistake. But...how many dumb people does it take to keep the old 8800gts's price steady since Christmas?  

Example EVGA 8800 640mb GTS $250.00:

http://www.newegg.com/Product/Prod [...] 6814130327

Example EVGA 8800GT $230.00:

http://www.newegg.com/Product/Prod [...] 6814130318

Example EVGA 8800 GTS (g92) $240.00:

http://www.newegg.com/Product/Prod [...] 6814130325

WTF, I guess they really dont want me to go SLI...i guess ill do what they want and save up for the 9800gx2.

Because 640 > 512 making some people happy to pay the extra money.

Do people not know how much better the gt is or the gts(g92) for that matter? I just don't get it. The stupidity hurts my head.

I'd have to make the assumption that since most manufacturing processes are geared towards the G92 there won't be much of a drop in the G80 price.  Plus what pauldh said, the average user doesn't know the difference and assumes more is better.

Its kind of like asking why Pentium 4's still cost more then most Core2's

I think the G80's cost more to make too with its larger die size...

---------------
http://tinyurl.com/26uxxb - Core2 Temp Guide
http://tinyurl.com/cj3pw - VGA power use

Those cards were probably manufactered months ago and sold at a set price. I'm guessing those cards are close to there cost. Even the 7800GTX up until a few months ago was still $400.

Heres one reason http://www.tomshardware.com/forum/249224-33-good-card We were having a hard time just TRYING TO EXPLAIN whats going. Theres ppl out there that dont know, and sharks out there getting fed

They wouldn't be happy if they compared the overall game performance:

http://www23.tomshardware.com/grap [...] &chart=318

ryanthesav, I don't know as much about SLI as I do Crossfire. Can you get a 9600gt to work alongside the 8800gts 640? Those might actually be comparable:

http://www.tomshardware.com/2008/0 [...] age13.html

It seems just enough below the 8800gt to work with your card.

 
SLI only works with cards that have the same chip.

Simply
 
Even you half-answered your question. Those old GTS cards were amazing at their time and they cost a lot so they dropped their price incredibly after the GT and new GTS cards came to light. Some even decreased $100 on their original price.
How come they still higher than GT and GTS? Because like you said some people still buy them and also because they just cant lower their prices to $100 since again, people keep buying them.
 
Finally and dont know if important but worth mention it. Because 65nm chips are cheaper to make than 80nm which most 8x00 series are made of.