For basic sciences, I think that pharmacology and physiology are the most important, definitely. Learn how to read EKGs as well or do it during clinics (I personally think you should do it during basic sciences though).
For clinics, anesthesia (duh!), critical care (preferably a closed unit), also maybe cardiology and pulmonary. Now radiology... I read that also, but I really cannot see where it will possibly be helpful in anesthesia, except in critical care...
I took a cardiovascular anesthesia rotation and learned just a ton of cardiopulmonary physiology, so I would highly recommend that as well.