Motherboard- I'd recommend an Asus only because thats what I used and thats what people recommended for me.
Like someone else said, plan on getting fans if you're going AMD. Thats the only thing I hate about my comp because its loud with all those fans blowing.
And before you start building your PC, I recommend that you read the whole MOBO manual so when you start your project, you will have an idea of what to do and how to do it. Asus boards comes with real in-depth manuals compared with my old PC mobo manual.
As for ebay...I got some of my stuff off of ebay. Just make sure that you know what you are bidding for and check the sellers feedback. I think you can save some money by buying off ebay, its just if you trust the product or not because you usually won't be able to return it. I think shopping around on the net can be really beneficial if you take your time and know exactly what you want.
Just my 2 cents.