Diddlebug is a post-it note like program, I use it to keep track of all my patients IV rates, meds due (the program allows alarms to be set), vitals so that I can finish an entire hall, then go chart them, etc. Its an great time saver for me. I have thought about getting patient tracker, but on a student budget, its not workable
Although i have heard many good things about it.
Personally, for those of you who are wanting a good model to buy, Handspring visors are the most expandable. Memory, digital cameras, MP3 players, cell phones, they all can be plugged right in. Palm Pilots are ok, but not as expandable. PM me if you want their website. Also, check on ebay, they have a lot of PDAs on there for very reasonable prices.