Best expansion for a game?

What is a game that absolutely should not be played without it's accompanying expansion?  Some of my suggestions:

Are there any others you would recommend?

2 points by BoardWithRules - updated 6 months ago | 1 comments | report | subscribe

FirstJohn318 10 months ago | 1 point[-]

Dominion, Catan 5-6 player expansion, Carcassonne at the very least you need the expansion with the builder (I forget its name though), Merlin, DixIt at least one expansion is necessary.