As far as I've been able to tell, there are no distinct rankings of HCI programs, but CMU, Stanford, Georgia Tech, and MIT have some of the best-known ones (I'm sure that I missed some big examples- anyone have any other suggestions?). It's hard to compare the programs to each other since they all specialize in different areas (MIT focuses on creating awesome new technologies, Georgia Tech has a bunch of topic-centered labs but doesn't do as much with design, etc.)- you just have to look for the program that fits you best.