Running until January 3rd, there is a MASSIVE sale on Steam, with games ranging from 10% off to a ridiculous 80% off. Of course, the part of the store we're interested in is the Indie section, and it does not disappoint! There are some incredible deals in there to grab. I've picked out a bunch which I believe are essential purchases (unless you already own them, of course!) and they go as follows:

Defense Grid: The Awakening $2.49
Braid $2.49
Trine $7.99
Audiosurf $2.50
Eufloria $9.99
Crayon Physics Deluxe $9.99
Time Gentlemen, Please! $2.49
Osmos $4.99
Cogs $4.99
AaaaaAAaaaAAAaaAAAAaAAAAA!!! $7.49

These are my must-have picks - check out the Steam store for even more amazing indie deals.

In addition to the Steam sale, here's a bunch of other deals worth sticking your nose in:

And Yet It Moves 50% off
Immortal Defense Pay-Whatever-You-Want Sale
Tale of Tales sale
Irukandji and Bullet Candy Perfect for $1
Aquaria 50% off
Grappling Hook 25% off (with coupon code BMWS000H3)

Go forth and spend your Christmas monies!