if you look around or do a search on sdn, there are a few threads dedicated to free pda software....for ped's I recommend using program that lists vaccinations (mine is called "shots") and something called 'peds omnibus', which will give you a concise list of expected vitals per different ages, milestones, etc etc.
make sure you get a pregnancy wheel program, much quicker than the real wheels you'll see on the rotation.
there's also a program called Breast CA which has Gail and Claus model risk assessments for your patients - this will definitely make you look like a star if you assess some of your patients' risk levels
i second the shots program it's called "shots 2006" google it and download