The ATI ones are popular with Mac Pro 1,1 users because their more modern cards still have working EFI32 boot screens. The newer Nvidia EFI cards don't show a boot screen on a Mac Pro 1,1.
Yeah, after looking over what's out there, I think I'm going to go with an ATI 5770 PC version. They seem to be plentiful, relatively inexpensive, and I don't need the boot screen.
If I ever change my mind I can always flash it, too.
Looks like there is a cottage industry of sorts on eBay of people selling flashed "Apple" versions of these for about twice what the PC version goes for...
MacDann