I am a big fan of the Nomad hand held x-ray device from Aribex. Interestingly the inventor, Dr. Clark Turner started out looking for a completely portable x-ray unit for use in missionary work. Nomad can be used in mobile clinics, nursing homes, hospital wards, missionary work, and even forensics.
However it is also great for use in a dental office. A single Nomad can take the place of at least three or maybe four wall mounted units. That means not only is it more flexible but overall it costs less.