For small amounts I'd suggest somewhere like BitBargain. Other sellers of coins are usually interested in buying in larger quantities too. For e.g. check out: the footer of bittylicious.com, they're buying. Failing that, you could always just use mtgox and place a high sell order when prices spike. Last night would have been a good time to do that with the increased value. I'm fairly new to trading bitcoin, so perhaps somebody could give a more informative answer than myself