When my nephew was flooded last month, I helped him paint and he gave me most of his cabinet doors. I painted one and put it in my kitchen: It is so handy for leaving notes for loved ones, and to myself. I never knew how handy a chalkboard in the kitchen could be! The one I made for myself was a good size to hang vertical. Many of the doors I got from him were so skinny that they really need to hang horizontal.
See other great chalkboard ideas here