Blizzard says that the mods: Aiur Chef, Left 2 Die, and StarJeweled have been "polished with improvements and bug fixes, plus they now feature official achievements complete with brand-new avatars to unlock".
Here's a brief summary of what to expect:
StarJeweled: Pit your puzzle-solving talents against your opponent's. Match jewels to generate resources - and spend them to attack with StarCraft II units, countering your adversary's forces and destroying their base.
Aiur Chef: Gather and mix exotic ingredients in a cooking race against your opponents. Choose your recipes carefully to achieve culinary dominance and be counted among the most hallowed chefs of Aiur!
Left 2 Die: Working together with a partner, defend your base from onrushing zerg infested. Protect yourself from the relentless hordes during the night, and build up your forces to strike back during the daytime. Cooperate, or measure your survival in seconds.
The mods are accessible on the Starcraft II mods page.