What is the best processor for my ECS Elitegroup NF-MCP61 motherboard?

You need to know bus speed and socket type for this motherboard, It looks like it is an AM2 socket, so the only processor available on newegg is the AMD sempron at 2.2 GHz for $29.99. I'm not sure about the bus speed of the motherboard but since it is only .4 Ghz faster than what you have I imagine that it will work just fine. If you are upgrading the ram keep in mind this processor requires ECC memory.