Well, the first thing I would do is drop to the X4 955. There isn't any real difference between the two other than a slight factory overclock and $20 bucks.
For the board, I'd defintiely get a Gigabyte GA-790XTA-UD4. It's decently priced and a great board.
I should also point out that starting a build with Crossfire isn't that great of an idea. I'd spend the same amount of money and get a HD 5850 (like in [url=this combo with the board
]. That will be powerful for the majority of games and still leave an upgrade path for you later.