I signed with the Army Reserve Medical Corps.
They gave me a monthly stipend of nearly $1400 and incrementally have paid off 50k in student loans (be aware: the repayment amount is TAXED, but it still comes out to close to the 50 they promise).
For their assistance, I will be in the reserves for 2 years for every year they assisted me. Thus, I owe 6 years once I finish residency (in two months).
Reserve duty comprises 1 weekend a month and 2 weeks a year of training. I hear there are ways to get out of the weekend a month stuff, but I wouldn't count on it.
You can also get called up for active duty. If you do, it can only last for 90 days, plus a few weeks tacked on to the front and back of that for "processing" (which, frankly, doesn't sound pretty). If you have been called up, they can't call you again for a year and a half.
This arrangement precludes you working in many small or solo practices, but shouldn't be a problem at all with a mid-large practice or HMO. And it will actually help you get a job if you want to work as a civilian contractor with the military.
Based on my research, the other branches have similar programs, but the Army is the most lucrative. It is also the one branch where you just need to plan on getting deployed at least once, probably twice. Personally, I think going to theater for a few months will be a pretty cool adventure. If that kind of thing sounds like hell to you...be cautious about signing. Well, be cautious anyway.