I'm a big fan of internet challenges. I don't think they have the ability to completely change your routine and/or life permanently, but I think they're encouraging as hell and I'm sure there's at least one out there for anyone who's looking for a change in some aspect of his/her life.

Other than fitness and food challenges, it never occurred to me to try and find some more creatively-charged ones. I stumbled across this one on a now-defunct WordPress and I think it's a great one to take on when you find yourself in a writing rut.