What Classes You Should Take
New students often ask this question, and it's difficult to answer. It depends on who you are, what your background is, and what research areas you are interested in currently.
First of all, be sure to register for Ph242ab. This is the only required course in the physics graduate program, and all students should take it their first year. The course is easy, fun, and introduces you to some of the faculty and research that is being conducted in both in the physics department as well as other options. This course comes with free lunch!
Second, you may want to consider taking some of Ph106, Ph125, Ph127, and/or Ph129. These courses teach you basic physics -- mechanics, E&M, quantum mechanics, statistical mechanics, and math methods. If you did not do so well on the placement exams, consider that a clue that maybe you need to brush up on these basics. However, know that Ph106, Ph125, and Ph127 are essentially undergraduate courses.
If you have already taken similar courses at your undergraduate institution, these courses may not help you much with the basic written exams. You might do better by skipping ahead to more advanced (and interesting) courses, and studying independently for the exams. You have to decide. For help deciding, ask some of the more senior students. Note that Ph125c often contains fairly advanced material, since most of the basics are covered in Ph125ab--check with the course instructor for details.
You should also know that taking any portion of Ph106, Ph125 or Ph127 will NOT by itself prepare you for the basic physics written candidacy exams. The exams are difficult and you have to study for them.
Finally, take some advanced courses that will satisfy the Advanced Physics Requirement. Courses are described in the Course Catalog, also check the course substitution list for the Advanced Physics Requirement. You might especially consider Ph135 and Ph136, which are survey courses covering a wide range of physics. Here again, ask other students about the courses and professors; remember, however, that opinions vary widely -- often a course is rated both very high and very low by different people.
Physics graduate students are allowed to take any course pass/fail, if the instructor permits, including those taken in satisfaction of the advanced physics requirement. One should note, however, the constraint that the exercise of the pass/fail option (in a course that is not already designated as pass/fail) is limited to two courses per term.