Fitmedic,
I've added 2 inches onto my thighs in the last few months. The basis for my hamstring routine is... SPRINTS.
I run 5 sets of 200 yards in the grass before I go to the gym. (The I start my gym work with 5 sets of 5 on squats.)
I trained at Gold's Venice for 10 years. I know many of the top pro bodybuilders... male and female. Many of the old guard swear by sprints as the top hamstring builder for mass.
I will admit sprints worked for me... much better than leg curls ever could.