Phi Beta Kappa, if you get invited, is worth joining. It's nationally known and very prestigious.
Other than that, if there is an honor society for those in your major it might be worth joining depending on what the chapter does at your school. Talk to a current member first. Some offer tutoring, a collection of old exams, etc. And also the chance to get to know the better students in your major (if you're at a larger school where classes can be large).