Any easy ab workouts alternative to sit-ups?

I'm just starting to really care about getting in shape and I'm still pretty squishy and not really flexable. Whenever I try sit-ups and curl-ups I end up hurting myself and it hurts my self-esteem then I get all mopey and don't do anything. Are there any exercises that are better for beginners, something I can use to tone myself until I can do a proper sit-up?