From what I understand, the active ingredient in Carmex, camphor, is actually a DRYING agent. I use it sometimes, and it helps. Plus, the menthol numbs those lips right up so you can't feel the pain anyway.
My wife swears by it.
I found a new weapon against cold sores (I get MANY): pure aloe vera. Try it - no kidding. Aloe vera helps prevent chapping too, but not as well.
Careful not to use too much of anything - they all "train" your lips to produce less moisture.