Just as a side note - Kirito-kun seems to be advocating the purchase of the cheapest mainboard possible... don't do that, lest you wish to risk poor performance.
The motherboard connects all the components together and feeds them electricity, you don't want that part to be crappy. You can squander on some less important components like the disc drive or the case, but the components that are directly responsible for the performance of the rig have to be appropriate.
Crappy motherboard means crappy capacitors and crappy capacitors mean poor current stability, overall instability of the rig and terrible overclocking prospects, if any at all. A mid-range PC requires a mid-range motherboard, plain and simple.
Right.
Brands to avoid:
Biostar, ECS, low end ASRock.
Chipsets to avoid:
Anything below 970 for AMD
B85/B75 for Intel and lower.