medscape app is my fav, followed by wikipedia. meddcape gives you a whole lot about specific drugs as well as a wealth of information on just about every clinical entity you'll need to know about. If you have access to it, uptodate is great for general info as well. You'll want to read up all your patients conditions and these are great for that.
honestly I haven't really found the need for many other apps during third year though. You'll want to download a good game to kill time with. Also, there are pdfs of texts and stuff you can throw on your iPad to keep in your coat and study for your shelf a couple minutes during the day, so one of those might be good if you can afford it