Don't buy anything. You'll open any big book once or twice and then be stuck carting it around.
In med school most of the books I found helpful were the slender review books available for between 20 and 30 euro (or used for a couple of bucks). If they were light on material I'd head to the internet, library, or powerpoints from class and annotate.
Reference books are a waste of money given libraries and online resources available to a student for free.
I guess there are a couple of exceptions:
Clinical Examination, Talley and O'Conner
Clinically Oriented Anatomy (though the set of flashcards might be of more value to you than the book)
Clinical Microbiology made ridiculously simple, Mark Gladwin and Bill Trattler
I also used ipod touch apps a fair amount. (MedCalc, Davis Drug Guide, a few other free ones)
The at-a-glance series is great in upper years as is Toronto Notes.