I have the following that I've used pretty regularly:
1) epocrates essentials - super useful quick drug/lab reference, $$ (our school has free subscription)
2) dyna med - great for management/workup of different diagnoses, more detailed drug information, $$ (our school has free subscription)
3) hopkins abx guide - can look up by type of infection or type of bug which isn't in the other drug resources, $
4) diagnosorus - great for generating ddx's on internal medicine, free
5) mediquations - great resource for all those equations that you won't remember at 5 am, cheap
6) medabbr - medical abbreviations, great for deciphering charts, cheap