DogeCoins can be sold at CoinedUp which is a crypto-only exchange. You could also try selling your DogeCoins at /r/dogemarket, the market section at Doges.org, or in IRC at irc.freenode.net #dogecoin-trade.

InfiniteCoin can be traded at cryptsy.com.

DogeCoin may be on Cryptsy soon because many people have contacted Crypsty about adding the coin to their service, so if none of the above works for you then hold for a while!