Litecoin and DOGE maybe? You can trade both of those with ease on all the exchanges. The other ones? Forget about it, the markets are thin as can be for the most part. Even the market for Dash on Yobit is thin, though I know they're a relatively small exchange. I don't think 99% of altcoins have a future outside of the initial pump & dump anyway so most aren't worth mining.
LTC/Doge got a high difficulty by now - no?
How about Ether? Does that have a high difficulty?