If you want two nVidia video cards then I'd say eVGA 680 A1. For two ATI video cards, P5W-DH is still a good option, or GA-P35-DQ6, or wait a bit for an X38-based motherboard.
If you only need one video card, you probably want something based on the P35 chipset. Some of the most popular models are Asus P5K, Gigabyte GA-P35-DS3R or GA-P35-DS3L, aBit IP35Pro.
The differences in performance between motherboards are negligible. I've seen lots of reviews where you get 103 fps instead of 100 fps if you change motherboards, etc - you wouldn't notice the difference.
Some boards overclock better than others. Those I mentioned are good at it, by the way.
Instead of looking at performance you should look at features. For example decide if you need two video cards (and, if yes, what kind - ATI or nVidia) or FireWire, or wireless, etc., then pick a motherboard that has what you need.