EVGA GeForce GTX 750Ti 2GB GDDR5 Graphics Card

It should work with fully updated Lion or later singe Googling shows others have used it.. You will not get any screen display until the drivers are loaded unless the card is flashed for a Mac.

ANY dual-wide card will fit. Even the Apple ATI 5770 is dual-width

The question is what OS version, and does the eVGA use two 6-pin power feeds, that is more important.

And everything you want to know about Nvidia cards

http://forums.macrumors.com/showthread.php?t=1440150

Will work in that machine, but needs 10.10 AND the Nvidia Web Driver.

(Will have no boot screen unless you get an EFI one)