I'd like to vote for Darkcoin and Vertcoin. Darkcoin, because it offers better anonymity. Vertcoin, because it is the most ASIC resistent coin, and has a means of preventing the development of ASIC's in the future. I think that gives it long term potential.

Third, although it isn't released yet, it would be great to have Zerocoin added when it gets released in May. It will offer even better anonymity than Darkcoin, and Zerocoin has been in development for quite a long time now, with many very talented developers. There has been a lot of buzz around it for a good year now.