The rear delts usually get neglected, but this is a pretty easy fix and one you can do at home on a daily basis. The band pull-apart will bring your sad little finger-sized rear delts up to snuff quickly.
You don't need a heavy-duty resistance band because you're going to keep the reps high. Rock bottom rep range is 20, done for 4-5 sets daily.
Charles Poliquin is a genius when it comes to devising innovative, painful exercises and his One-Arm Barbell Eccentric Curls are no exception. They're guaranteed to hurt, along with eliciting stares from other gym members.