I only have experience with a Palm, but really like it. Mine is the Palm TX and has plenty of memory. If you need more you can always add a card in the expansion slot.

You will love your palm and find you cannot go without it. Mine always lives in the side pocket of my pants and I am absolutely naked without it! You will save so much time looking up drugs, calculating rates, or reviewing a procedure.

Skyscape offers a good selection and many of their titles also include a desktop version so that you can do a little research at home when you need to. Epocrates is also fine. You should check with your employer as some hospitals offer a database for their employees. I was able to download, entirely free of charge, a great drug handbook, lab values database, and one with diseases and conditions.