Why are there price supports for milk, but not for, say, steak? I don't know; the just-so story I suggested was that milk is sold primarily directly to consumers, who are a very dispersed interest group (so they find it difficult to organize to oppose the regulation). Steak is an important input for many restaurants, so perhaps they form an effective counter-lobby against ranchers. Bryan Caplan's answer to why such a clearly inefficient regulation would exist would be (in part) "voters are rationally irrational and support the policy", but I don't think that's true here. I don't think most voters are even aware milk price supports exist. It has to be some sort of classic lobbying battle.
Is there regional variation in minimum wage laws that correlates with homelessness rates? One student said that she had lived in Hawaii, where the minimum wage exceeded the federal wage and homelessness was rampant. I guessed that if one were to run the data, one would not find a relationship (although I don't think there'd be a causality problem--how would high rates of homelessness cause a higher minimum wage?), but it sure would be interesting to check.
Why do some cities have rent control, but not others? Why New York and Santa Monica, but not Atlanta? I don't really have any good answer here. Anyone have any ideas I could run by the students?