not if you have any back issues.
Hills on the bike are good too. We're not all runners.
I did something on the stability ball recently (hadn't done it for a while because I forgot about it).
It's going into my regular rotation.
Hamstring Rolls(got the right link this time)
Back Extension
The one I reeaally wanted to show you I couldn't find a photo of.
The starting position is similar to the back extension but roll forward on the ball until your hips are centered and hands are either on the floor or holding onto a chair or end of a weight bench. Raise your feet off the floor (it doesn't have to be far until you start to feel this). Open your legs into a V, bring them back to center, lower and repeat.
If you don't feel stable enough on the ball, you can also do this one with your hips on the end of a weight bench.
The advantage to doing these on the ball is that you're also building core strength. A twofer!