Sunflower seeds (shelled, it's fun to open them, plus you don't end up eating as much)
Carrots, celery and other veggies (maybe a dip, hummus?)
What I do with beans is usually rinse and drain the canned ones, spice them with a bit of oil and fav. spices then put them in the oven on low, they just roast and the oil kind of dries up but they become crispy (with a tender centre) little snacks. I can't imagine they'd be too unhealthy.
I like walnuts and dates as a snack, but walnuts can be fattening. A bit of nuts should be ok.
Raisins are another one of my favourite snacks, and they're healthy too.
Something a little more troublesome but worthwhile is a yam/sweet potato, I think it makes a great snack, I wrap them up in a foil then bake at 400 F or so until it's tender, the juices/sugars tend to come out and become a bit thick and carmalized on the bottom, a good source of fiber, and makes a nice "sweet" healthy snack.
Popcorn was another good suggestion. Other seeds like pumpkin seeds or a healthy trail mix is good.
And another weird idea that I sometimes enjoy are peas, just boiled (the frozen ones)