What GTS 250 cards will sli with an EVGA 9800GTX+?

If you mean brands,then any brand should be fine,and yes it should work as long as both have the same memory
http://www.firingsquad.com/hardware/msi_geforce_gts_250...
"NVIDIA says the GeForce GTS 250 will run in SLI with the 9800 GTX+, but the two cards must have the same amount of memory in order for SLI to function: you won’t be able to pair a 1GB GeForce GTS 250 with a 512MB GeForce 9800 GTX+."

In the past ( pre8800 )a 512 card and a 1gig card could be sli'ed together but only 512 memory would be used, no ?..... didn't read the link.

Correct.

i knew that different brands would work but i read somewhere they might have to have the same amount of 6 pin connectors. it would probably be best to just buy one of a better card and sell the 9800.

When did it change from having to be the exact same chip ? I know most of the line up is just rebranding but i could have sworn last time they rebranded the cards didnt SLI ?

Mactronix

I thought 8800GT/9800GT could SLI each other.

Really because I heard they couldn't be

Although they have the same specs,in general you can't SLI them however i have seen some users reporting that with flashing a 8800GT's BIOS to a 9800GT's BIOS you can SLI them,but its risky and not recommended really