The glute ham raise is a unique and effective exercise that targets your entire posterior chain, specifically your butt and hamstrings. It is a very "functional" way to train your hamstrings, and hits the core hard also. It also fits in nicely with my mission to incorporate more 'natural' or body-weight type exercises into my program.
However, not everyone has access to a GHR machine, so this video outlines some alternatives. Here is another piece of portable equipment I found as well: