Several schools have loan forgiveness programs to students who go into public service or non-profit jobs whose salaries just can't compete with "traditional" paths like banking or consulting. Stanford, Haas, Fuqua, Yale and several other top-tiers have such programs, though some are "matching" rather than outright forgiveness.
As for actual career paths, it definitely takes more creativity. As I was discussing with an adcom member at Fuqua recently, non-profiters at B-school are by necessity less risk-averse than many other applicants. We really do need to work harder to find a suitable job. Your dream non-profit doesn't come to recruit.
My goal is to start my own organization; a "social enterprise," not really a non-profit, since I plan to structure it so as to both create profit and return value to investors. A friend of mine actually has a similar gig running now in Rwanda and Kenya (One Acre Fund - started by a Kellogg MBA!). If you don't wanna go start your own thing, you can hook up with a global non-profit like CARE, PATH or Amnesty, just to pick a few. Even better, you could look into getting in with a smaller up-and-comer. And there's a whole field of microfinance organizations getting started out there - though be warned, they often have tons of well-intentioned MBAs applying to help, so experience in the field is pretty much a prerequisite.
And finally, you could just hook up with a foundation or a corporation's CSR department somewhere until something comes along...