I acquired my (very small) BTC stash via selling stuff on the eBay clone BitMit; it was starting to get traction before the site owners decided to shut down / sell (its fate is still uncertain).

There are two others, CryptoThrift and CoinGig, but their transaction volume is still relatively low. It's a gaping hole in the market right now (and that's considering that eBay itself has been begging for a disruption for years).