In The Binding of Isaac, some of the items that you can pick up are special numbered Tarot cards with different special effects when you use them. Some of these trigger events that I don't want to happen; I used The Emperor under the impression that it would save me from peril but it took me straight to the boss of the floor. So in order to avoid these kinds of situations and use each card appropriately, I'd like to know: what does each card do?
The Binding of Isaac wiki's got a pretty comprehensive (if slightly generalized, and minorly inaccurate) list. Remember that all cards are a single use item, so once they are used they vanish.
Tarot Cards II, III, XVII, and XIX were added in a patch on November 1 2011.