Obstacle Smasher — removes all obstacles from the board.
Double Wild Card — adds two Wild Cards to your hand at the start of a level.
Color Chaser — removes all cards of the same color from the board.
Undo — gives the ability to cancel a turn for a certain amount of time, or has a limit on the number of uses.
Replenish — gives the ability to get extra cards if there are no cards left in the starting deck.
Wild Card — gives the ability to get a Wild Card for a certain amount of time.
You can always read about additional boosters before starting a level by pressing "i" in the level window.