Throw in over-pairs too.

It depends on how much money was left behind after the pre-flop action and the number of players that saw the flop. If the pot was raised pre-flop, the stacks are short compared to the blinds, and/or you're dealing with a very aggressive opponent you should be going all-in with TPTKish hands or worse! As the players get more passive, stacks taller, the pot unraised and as more players see the flop then your standards for hands you're willing to go all the way with need to raise.

Yet another reason not to limp with hands like ATo, QTo, etc...