how much are you willing to spend on it? Do you want to go on the cheap or do you want one that will be a build for the future?
There's a GIGABYTE GA-880GM-USB3 AM3/AMD 880G/Hybrid CrossFireX/USB3.0 MATX Motherboard MB or this GIGABYTE GA-880GM-USB3 AM3/AMD 880G/Hybrid CrossFireX/USB3.0 MATX Motherboard MB, either for only $90
They are both am3 and support the ddr3 memory I think you already have. But you will need to include a video card with it. We will need to know exactly what cpu you already have to see if it matches these motherboards.
If you want something that has onboard video that's something that we'll need to know.