Mining it for fun as I type. As much as I would love to joke Altcoin to actually become something and be able to trade with it, I still think it will die off in about 2-3months. And that estimate is being optimistic.
The coins I think might hold some value in the future are:
Quark GalaxyCoin GrowthCoin GridCoin
And of course, Dogecoin. Can't leave out the Doge. However, I currently mine Litecoin and Feathercoin. I see those two as having the most potential for use beyond simply exchanging them on currencies in hopes of making some quick cash. These coins are already being decently used for real world transactions for goods and services and I am putting some faith in them.
GridCoin is promising because it actually contributes to society as a whole. Instead of crush arbitrary numbers that do nothing at all.