Yale. You either get "Pass" or "Honors". And you could probably fail a class, but I doubt that happens very often. Realistically, anyone who gets into Yale is probably going to put forth some effort, but there isn't a whole lot of pressure to go nuts. I mean, even if you get all "Pass" scores, you still graduated from freakin' Yale Law. I'd guess that getting a lot of "Honors" would give the top Yale students priority for the super prestegious clerkships, like working for a Supreme Court justice. But really, as long as you graduate and pass the bar (as over 94% do- which is actually disturbingly low [it really should be 100% on the first attempt] in my opinion considering the outrageously high GPA and LSAT scores of their student body) you'll have an enormous advantage over the graduates from almost every other law school.
I think there's another college in CT that doesn't give letter grades, they have detailed comments instead. But that school ain't no Yale, so it probably hurts their graduates a lot, since there's no "top of the class" for the law firms to immediately whisk away to hundred plus grand jobs- they have to look hard to find out who's the best, and looking hard is very expensive compared to looking at a nice rank % or GPA number.
My understanding is that a curve simply defines where the median grade is. The score where you'll be in the top 50% of your class. So, every school that has a grade based ranking system has a curve (effectively). They just might not try to influence where that curve is.
So what I think you really want to know is "What are some law schools that have their curves set very high?" For those, you'll have to call 'em up and see if they'll tell you, or ask students. But even if the curve is 3.5, being at the bottom 25% of your class with a ~3.25 is not going to impress your prospective employers (unless you went to a top school).