I gave a whole lot of books to my sister to give to the people who give books to the homeless. SHe decided to sell them on Ebay. Didn't work - got 99cents for a few of them and then had the hassle of postage etc.

I sold 3 x bags of maternity clothes (sorted into size and season ITMS) and two of the bags went for about $30 each and the other went for about $7. I was happy.

My kids clothes i have so far sold and given away on BB. Just sell the really good stuff and thrown in the rest for free. I don't have any friends with boys younger than mine. In fact, in my mum's group they tend to give me ALL their boys clothes, so i have a lot more than I'll ever need!

I don't think you ever get their value back, and as long as you aren't going to get disappointed, then you'll do ok. Apparently Gumtree is good too, i've never used it.
I just put the money in the boys bank accounts. Then it's all worth it, because it's their education fund.