I currently have a Sapphire 6870 GPU and are going to get either a I3-2100 or a I5-2500K CPU and I need a new microATX motherboard for gaming. I'm also going to grab some new RAM and suggestions on those would also be appreciated.
I have built many Micro ATX systems as well as full size. My personal favorite is an Asus Brand. Other people have their preferences and I'm sure they are good. This is a proven board. I don't know if you have a budget but there are plenty of gaming MicroATX motherboards to choose by Asus. I can suggest a few if I have an idea what you wanted to spend.
For memory I suggest any good 1600Mhz stix. THis motherboard runs that speed natively. Here is a choice or two: