If you have Palm Os, Windows mobile, Blackberry or an iphone/ipod touch, you can get free Epocrates Essentials at
for a free med student license for Epocrates Essentials for 1 year. Only through today, Weds 3/18. You have to register and watch a short video, but otherwise, you get $150 worth of the software free.
I believe you could also download it to iTunes, then transfer it to an iPhone/iTouch later.
From the website, they intend this for med students (and ask which school you go to, etc), though I’m not sure how much actual validation is involved.