I have the "Psych Drugs" app (I believe it's free though I got it quite some time ago so that may have changed). It has an extensive list of psychiatric drugs (in alphabetical order). When you tap any one drug, it opens up and shows you the generic and brand names, what class it is, the indications for it, all the dosages, the maximum daily dosages (separated for adults and children), and also the half life. You can also create a "favorites" list for any drugs that you might need to reference frequently. There is also a search feature.
A good stopwatch/timer is key, though I believe that is pre-loaded on all iTouches/iPhones (just select the "Clock" icon). One app that is not psych-related at all but I have found to be helpful is "GasBuddy" - I believe this one is free too. It tells you the price(s) of gas at each of the stations near you (and/or any city/zip code you wish to enter). All the prices are submitted by other users of the app and they seem to expire after a certain amount of time has passed since the price was reported (seems to be somewhere in the 36-48 hour range). You can enter gas prices very easily and when you do, you earn points. Every time you earn 1,000 points in a week, you can enter a free drawing to win $250 in gas.