Please find below a list of numerous exercises whereby the primary muscle group worked are the hamstrings (leg biceps).
The gym exercise demonstrations and descriptions provided (follow relevant links) should help you to better understand the exercise (in order to perform it correctly) and for who (i.e. what sport) or when it may be beneficial to perform in training.
Remember, many popular sports (football, soccer, rugby, running, cycling etc.) are very demanding on the quadriceps (the opposing muscle group to the hamstrings). Although sports-specific training will naturally encourage you to train the quadriceps muscle group harder, to avoid possible injury your supplementary training (weights) should help to iron out these imbalances - train your hamstrings!
For ideas on sensible gym workout routines, please see 'Workouts', or considering the purchase of the bestselling Gym Professor publication Gym Workouts: Maps to Success.