Do not know if you will be eventually wanting to do Sli. But this motherboard looks like it has the space you need and it meets your other critera's.
BIOSTAR TForce TF7025-M2 Socket AM2 NVIDIA GeForce 7025 Micro ATX AMD Motherboard - Retail $65.99http://www.newegg.com/Product/Product.aspx?Item=N82E16813138074
Or you could go with this 590 series motherboard that is SLi with both PCIE running 16x and put your 8800gts in 2nd slot. It is a little over your $100 limit by $20 after mail in rebate. But Evga motherboards are getting a rep for being very OC'able.
EVGA 122-M2-NF59-TR Socket AM2 NVIDIA nForce 590 SLI MCP ATX AMD Motherboard - Retail $149.99 ($119.99 after $30.00 Mail-In Rebate).http://www.newegg.com/Product/Product.aspx?Item=N82E16813188016
Hope this helps you out some.