Btc-e.com and bitfinex.com are probably most popular. Both offer short trading and also leverage if you want it. I prefer bitfinex as customer support is way better.
Bitfinex looks promising, and I will look into it later (though they don't trade doges, as I got it so far). I've heard not very good things about the Btc-e exchange (them seem to be keen on ruining their clients). Though, on the other hand, they are long enough in the trade (no pun) to just run away with money...
both btc-e' and bitfinex' support are not good, compared bitstamp and lakebtc.
Yes, but he was asking which exchanges he can short sell at.
No problem, really. It is always helpful to hear what other people have to say about this or that exchange. And, in fact, it was me who said that the Btc-e exchange has got a somewhat muddy reputation, so the answer is quite in tune...