Ken,
first and foremost, they suck in terms of good nutrition value.
but to directly answer your question...heard of protein powder? kinda like nestle quik powder, except it has a bunch of protein in it...not just sugar and cocoa.
well, a protein bar is the same thing...lots of companies make them under a million names. they all contain the same kind of whey protein powder, and other stuff to bind it together into a sort of 'candy bar' style product.
unfortunately they just aren't that great for you. usually full of simple sugars and fats...which aint' good if you're trying to lose fat off yer body.
there are recipes around here for making your own bars with protien powder, oatmeal, peanut butter, and a few other natural ingredients. Still not 'perfect', but considerably better as a 'convenience food' for those on the go.