I was wondering if there are any real benefits to joining AAPM&R as a student. Does being a member look good when applying for a residency? Thanks

I think it would show your interest in the field and I think many PDs do look for that in a candidate. If you decide to join, you should also try and make it to the AAPM&R conference. That being said, join because you want to and not because it might help your application. The amount that it would actually help probably isn't worth the expense.