To nullify enemy's combat ability by teleporting, the teleport would have to be an immediate action. That means that it can be cast even outside your turn, once per round, but not on the same turn as a swift action.
Much like a swift action, an immediate action consumes a very small amount of time, but represents a larger expenditure of effort and energy than a free action. However, unlike a swift action, an immediate action can be performed at any time — even if it's not your turn. Casting feather fall is an immediate action, since the spell can be cast at any time.
There is a wizard variant, named abrupt jaunt(PHB2), that allows this (int times per day) in exchange for your familiar.
Please make sure that Abrupt Jaunt is okay with your group before you take it, it is considered overpowered by many.
Alternatively, you can choose to ready a standard action to teleport away, using any such spell you know, if you wish, but you lose your standard action for the turn.
The ready action lets you prepare to take an action later, after your turn is over but before your next one has begun. Readying is a standard action. It does not provoke an attack of opportunity (though the action that you ready might do so).
You can ready a standard action, a move action, or a free action. To do so, specify the action you will take and the conditions under which you will take it. Then, any time before your next action, you may take the readied action in response to that condition. The action occurs just before the action that triggers it. If the triggered action is part of another character’s activities, you interrupt the other character.