I am a fourth year medical student right now with a BBA from the Ross School of Business at the University of Michigan. If you are thinking about Ibanking then your best bet is to not waste more time in medical school. Investment Banking is a very difficult field to just jump into, and I am sure you believe an MD is going to seperate you from the bunch. It definitely will make you stand out, good and bad. For one thing, the quintessential banker is one whose technical skills are top notch, and for you to have gotten this far along into medical school you can be honest in acknowledging that the training required for medicine as well as the practice of medicine requires little to no technical ability (save for radiology/rad. oncology).
This is a big knock against doctors, which is why consulting is usually the siren song that lures physicians into business. In consulting, the ability to problem solve, to manage crisis, to develop feasible solutions and develop strategy is required. I personally believe these are things doctors can just knock out the park.
As for the other poster who thinks that i-banking experience will influence the md/mba program....well yes and no, yes because it shows some diversity, but they could care **** about that. Someone with research experience in all honesty would probably interest them more, because it has more to do with what they want (research=grants=prestige). As for ibanking experiene for an MBA, a summer stint in banking is a laughable qualification. MBA positions are not given necessarily on what you've done in the past, but a lot of times on what this degree will enable you to do in the future. People go get an MBA when they reach a position at work where they cannot go further without more training.
I was in management consulting prior to medicine, in many ways I wish i never left. I realized that a person can be only one thing, I thought I could balance medicine/business, but I now realized you're either a doc or a business person can't really do both. Thats why i recommend if you feel you are a business person, that pursuit of being a doctor may just be a painful distraction. Food for thought.