Look at recent journal issues, and note the author's affiliation for any articles that you find particularly interesting. Attend regional or national psychology conferences. Talk with your advisor and letter writers. Good universities don't always have good psychology programs, so don't apply based on name alone. Get current brochures from many programs - don't rely on old information.
Most departments also have Web sites with lots of information.
Your best printed guide is Graduate Study in Psychology , published by the American Psychological Association, which lists all the graduate programs throughout the United States and Canada. The book provides specific information about programs, including the average GPA and GRE scores for the previous year's class, how many students applied, and how many were accepted. It also includes information about financial aid, tuition, deadlines, and internships. This information will give you some sense of how competitive you would be for getting accepted at a particular program. Write or e-mail the faculty you would like to work with.