Want to mix up your games of Small World?  Tales and Legends does just that!  http://www.daysofwonder.com/smallworld/en/tales-legends/

Rather than adding new races or powers, Tales and Legends is a set of cards that add a different "rule" every turn.  Usually these are in the form of world events, such as a plague that sets every active race into immediate decline at the start of that turn.  Sometimes it's an auction for something as simple as going first.

How it works:
Before the game begins, randomly draw a number of cards from the deck equal to one less than the number of turns in the game.  So if there are ten turns, you draw nine cards.

Stack the drawn cards face up on the "Upcoming Event" pile.  This allows you to see what is going to happen next turn, so you have some idea how to adjust your strategy.  Then between each turn, you move the top "Upcoming" event over to the "Current Event" pile and follow its instructions.  This way the first turn is normal, but every turn after that is special in some way.

This drastically changes the game, since it often prevents you from planning more than a turn ahead.  If you see the upcoming event makes mountains unconquerable, there'll likely be a rush to claim those regions this turn.

Although I likely won't be playing Tales and Legends every time I crack open Small World, it does a great job of keeping the game from getting stale.  It really can turn "killer combos" like Spiritual Ghouls into a liability.  I had Pillaging Skeletons and had to give them up the next turn!

Tales and Legends is a worthy expansion to Small World, and I highly recommend it.