The best site for medical software for Palm/Pocket PC/Smartphones is undoubtedly
Skyscape. They cover just about all specialties with lab/drug references, reviews, texts, etc. I'm in the process of trying to get the nursing program that I teach in to allow PDA's for use during clinicals for references rather than having to lug around multiple heavy books and we're working on getting our programs from Skyscape. I've been using them since I had my Zire 71 when I was in my MSN program.