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...
Yes, i had a bad experience with btc-e so I'll admit I'm bias. I still have a few hundred dollars in account there that I can log into and trade but it is impossible to withdraw because the email associated with the account no longer exist. (They require you to confirm withdraws with an email). My fault for the email but customer support will not help me with this. I've submitted dozens of support tickets and jump through hoops to confirm I am the owner. Even proved I had the same IP as when the account was open. All that to no avail. So I chalked it up as a loss. Shrugs.