Any cash limits? I'll bet they'll likely have most of the specific dermatology things they will need so I'd say just get them something nice that most anyone would appreciate. A night out to dinner, concert tickets (if you can find out if they're free ahead of time), etc.
It depends on how much you want to spend. A TUMI or Coach type of bag would be nice.
Depending on the situation, maybe personalized scrubs. I personally wear scrubs without my name, but some people like them I guess.