Dave asks, "So what schools would you say are good for public interest?"
Well, Dave, I think it depends on the region. (If you've narrowed your search to a region and want to throw it out there, maybe the commenters will pitch in.)
I'm certainly not saying you can't go to Stanford, Yale, or Harvard and work in public interest. You can, and people do. I'm sure that there's not a law school in the country that hasn't produced at least one public interest lawyer, or that wouldn't tell you on your tour "Oh sure, we encourage pro bono and public interest work."
But I think there's a difference between that and a school that has a reputation for public interest. There are schools - sometimes lower ranked, sometimes state schools, but not always - that put more of an emphasis on practical experience and have more graduates entering public interest jobs.
(You may run into the chicken and the egg problem here - do students in lower ranked schools go to public interest jobs because that's all they can get? Or do those students genuinely leaning toward public interest gravitate toward these schools?)
Any school can put the words "public interest" on their website. And most do. The best thing you can do is ask around the public interest community and see where people in the field of your choice graduated from. This may narrow your search even more - if you're interested in environmental public interest in a particular state, you may find that everyone in that field went to one particular school that's known not only for public interest, but also for it's environmental classes or clinics. Likewise, if you want to be a public defender in an area, ask a few PDs in that area where they and their colleagues went to school. In some states, you might get one big resounding answer and quickly realize that X Law School is the place to go, or, at least, the place they hire from. In others, there may be more of a mix. But it will give you a sense.
As far as what to look for in a law school, the words "public interest" on a website aren't enough. I'd ask the career services office how many graduates they placed in public interest jobs in the past year and what these jobs were. (Some schools take a much broader view of what qualifies as a public interest job.) I'd want to know exactly what, if anything, the career services office did to help these graduated get their jobs (or were they just particularly motivated, doing their own leg work so that the career services office could take all the credit?) I'd look at the classes actually being offered for a semester or two (as opposed to the classes that are listed in a catalog but haven't been offered in a few years) - if you've got an entire lineup of corporate law and it's variations, it's hard to call yourself a "public interest law school." I'd take a good look at the clinics and make sure there's one that fits my interest (I'm a big proponent of clinics), and ask how difficult it is to get into the clinic, and what are the clinic professors' backgrounds.
I'd ask whether or not they have a loan repayment program for public interest lawyers. But it's not enough to just have one - I'd want to know how many alumni are actually receiving money, how much they're getting, and what types of jobs they're in. Then compare the number that are receiving repayment assistance to the number career services says are working in public interest!
That's a lot of information. If you're looking for particular names of schools, leave a comment with the geographical area and public interest area, and maybe you'll get some replies.
I have to admit, I didn't know any of this when I was looking for law schools. In a lot of ways, I was like the know it all - I didn't know what else to look at besides rankings. But the difference is, I didn't have access to any real live lawyers who were willing to give me advice about law school. So, take advantage of what you've got.