This page links to a wide variety of tools labelled as encounter and dungeon generators and calculators.
It's mostly here because I keep losing the ones I want to use.
Generators create things for you, sometimes according to specifications.
Generators are cool, but not very meaningful. I find they're often best when isolated interesting components are used, instead of the whole.
Yours Truly - agnostic - Dungeon Generator : Not very useful; at the top of the list because I made it.
Donjon - Pathfinder - Dungeon Generator : Generates an entire dungeon. Useful mechanical tool; generates interesting treasure.
DMTools - agnostic - Adventure Generator : Of excellent worth for getting a solid outline and some good direction; conversely, has very little mechanical detail.