What is the best power-bar type thing?!

I'm looking for a power-bar-ish type of thing to eat while I'm running around during the day. I usually bring a lunch with me when I know I'll be gone the whole day (usually an apple and some carrots or broccoli florets), but I would like something to keep my metabolism moving in between meals. I'd prefer low calories, and I'm also looking for something with a little bit of protein in it, or some sort of health benefit from eating the bar. Taste is optional. Any suggestions? P.S. No Luna Bars. I hear they have estrogen in them and I don't want any of that.