They make you think you are going to use them alot, but you don't. They provide lecture notes and that is what you are tested out of.
I graduate in 3 weeks. I bought DiPiro, some huge OTC book, and Katzung's pharmacology book. Wait, I did use the DIH, so you might want to buy that one. I never used the OTC book, even though they made me feel like I would fail without it. Katzung's was used a bit to clarify things, but it is in the library and I believe online under MDconsult or somewhere. DiPiro is nice, but you can buy the "mini' Dipiro Pharmacotherapy Handbook, and it is a lot cheaper, easier to read, and cuts out all the extra crap you don't need.
What I would buy is a nice PDA and get Lexi-comps suite on it for a couple hundred bucks. That provides the DIH, mini Dipiro, and about 15 or so other good references. Then, you might want an actual DIH for all the charts in the back and also the Mini-Dipiro has a lot of charts and graphs that are not on the PDA version.
I will let you in on something. Almost any book you need will be in the library with multiple copies. They will be a year old or so, but not many changes at all. You can check them out for a month at a time, and if nobody requests them, you can keep them out the whole qtr. I know several people who did this and I actually did for the physiology book 2nd qtr.
So if I could do it all over again, I would buy lexi-suite beginning 4th qtr, DIH and the mini-dipiro right off that back, and nothing else. The PDA program is about $250 I believe, and well worth it. The DIH and Mini-dipiro are both about 40-50 bucks. So you should be good spending about $350 for the whole program. Lexi-complete, suite or whatever it is called, is well worth the money, especially for rotations.
Be ready for a lot of busy work. Things have really changed alot since I started three years ago. You are going to absolutely hate Intro to professional practice. When I had it first year, our class consisted of guest lecturers coming to school to tell us about different jobs in pharmacy, a nice 1 credit blow off class. Now it is non-stop busy work that I havn't heard any kind words about. Also, be ready to hear that retail is dead and that if you don't work somewhere in a clinical position, you won't have a job in the future. Just try not to laugh when you hear this. Get through the first year and it is downhill from there. Good luck!