I use half.com way more than I should. I purchase books, DVDs, and CDs from them weekly. I've never, ever had a problem. I just purchased season 2 of Curb Your Enthusiams - in like new condition for $20 and I got it in 2 days! Make sure to read the comments carefully, however. Sometimes they will say things like, "Does not come in originally packaging" or "CD does not contain liner notes". But I really, really like this site and eagerly recommend it!
Also, it's also easier than ebay in that you don't bid, you simply click on the product you want, click on the price you want to pay - and it's as simple as that!