A good motherboard to go with a Phenom II X2 550 BE?

Here is a nice budget gaming system in the recent Sept 2009 Toms' Hardware System Builder Marathon using the Phenom II X2 550 BE to give you an idea.You can check out their picked components.
http://www.tomshardware.com/review [...] ,2424.html
It would probably bottleneck the high end GPU cards (esp 2 high end cards CF'd) however choosing this budget CPU you want a balanced system.It didn't fare badly against these other higher end builds.
http://www.tomshardware.com/review [...] ,2427.html

Well I think that they chose that motherboard so they could run those ATI graphics cards in crossfire mode as inexpensively as possible.It was a good choice as they balanced the cost of 2 inexpensive yet potent ATI graphics cards.
These cards were of the last generation though (The Radeon 5800 series was released shortly after this article)

If you intend to just run one graphics card one could go for a less expensive 785g chipset based motherboard or a 770 chipset motherboard.One could opt for a single Radeon 5850 graphics card ($260) or a 5870 one (about $380) although the 5850 is more cost effective but a little less potent than the 5870 for a single card graphics system.