Discuss the different sizes. ATX, mATX, uATX, etc. Mention how important it is to match chips to sockets. There are AMD boards and Intel boards. I don't know how in-depth you want to go, whether you want to discuss the different parts of a motherboard. Northbridge, chipset, socket, RAM slots, I/O, all that stuff.
There are definitely some brands to try to avoid and ones to consider, although all makers have good and bad. Not all boards OC well. Some are reasonable OCers, and some offer rock-solid stable overclocking goodness.
Usually, good boards come from Abit, ASUS, EVGA, MSI, DFI, ASRock, etc., and usually Foxconn, and maybe Gigabyte, maybe Biostar. I don't know much about Elitegroup or other brands.
What else is there? I'm blanking.