There is also an instant exchange called
ShapeShift.io, the exchange rate might be little lower from the traditional exchanges mentioned above, although it varies from time to time but the convenience of using it makes up for it as you don't need to make any accounts or register anywhere, just have a dogecoin address, enter it and they will provide a bitcoin address to send BTC to, send the bitcoins you want to get exchanged and after the transaction receives 1 confirmation, you'll see your dogecoin in your wallet.
They also have other altcoins which can be inter-exchanged instantly. Check it out, I use it anytime I need to exchange my altcoins to bitcoins or vice versa.
