I'd suggest you consider getting a Nook instead of a Kindle.
First, because whenever you're in a Barnes & Noble's WiFi zone, the Nook treats it like a library and lets you digitally read any book in the store without buying it. This is awesome for studying - head to B&N, get some coffee, and read Harrison's without spending $200 on it.
Second, you can loan books to other people for free, which you can't do on the Kindle. So if you know someone else with a Nook in med school and you both want to go in on a textbook, you can each pay half and just share (although just like a regular book, you can't both be reading it at the same time - you have to switch off, so this is better to do with reference books or fiction).
Third, because the Kindle doesn't have full support of the open-standard ePub format (and probably never will, since it prefers to use its Amazon-specific proprietary format), but the Nook does. So if you want to download a ton of the free books that are being open-sourced out into ePub, the Nook will let you do that.
Neither has great availability of medical textbooks yet, but based on the Nook's early support of .pdf and free formats, I felt it was more likely the Nook would eventually have better support. It's anyone's guess, but it seems safer to me. It still uses eInk and is very easy on the eyes.