I second the ASUS recommendation from climbtree; I pretty much only use their boards. You will probably want a 790FX rather than the GX that he suggested if you are going to Crossfire as the GX limits PCIe bandwidth to dual 8x or 16x/8x (depending on the board) when running two cards, while the FX keeps them both at 16x.
Here is Newegg's lines of 790FX chipsets:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010200022%20107191003%201071933047&name=AMD%20790FXOf those, I own the M4A79T Deluxe, and I highly recommend it, but that is DDR3, so you will want to go with the M4A79 Deluxe instead for AM2+/DDR2. If you are not looking to Crossfire, the GX would likely be significantly cheaper and will allow Hybrid Crossfire with your integrated GPU.
You will want to also be sure that you get the SB750 southbridge, which allows unlocking of your other cores in less than X4 Phenom IIs. Go
here for more info on that.
Aside from ASUS, the other most recommended are Gigabyte and DFI. You can see the
AMD Dragon Club at Overclockers and see what everyone is using if you want more suggestions.