Portability and practicality make these products useful for the busy medical practitioner and student.   Products by Palm, Handspring, Casio, HP and others are growing in popularity as are software for them  (be sure to have enough memory on your device).  Here are some sights that we have found useful:

Applied Evidence Inc - "Innohep" calculator and Strep Throat Predictor programs

Blue Nomad - produces software fully compatible with MS Word, or to view Excel, PDF and even PowerPoint files.

ePocrates - an excellent Palm OS Clinical Drug Database (U.S.) that is useful and free

Handheldmed - patient-tracking, billing and other software

Patientkeeper - patient-tracking