Depends on what you want to test... Considering which part this is posted in, the 3dmark series is a nice way to test imo... (But the score there won't give you more than an indication of what performance you'll see in real games...)
AquaMark 3 should be out by now, so do a little google for that...
SiSoft's Sandra is also quite good...
If you search this entire board for "benchmark" "program" you should find quite a lot of others too...