http://store.steampowered.com
Steam has their Holiday sale catalog from Dec 20 - Jan 2.

Some of the games I seen that may be worth it:

ARMA 2 - $9.99 - I was thinking about getting this one. Anybody else have it?

Complete Battlefield 2 Classic Pack (pre-bc2) - $4.99
- BF2
- BF2 Special Forces
- BF2 Euro Forces
- BF2 Armored Fury

Fallout : New Vegas - $29.99
*If you own Fallout 3 on steam you get $5 off making it $24.99

Also they have a Crapload of packs (all game packs)
- Rockstar Complete Games Pack $39.99
- THQ Complete Games Pack $49.99
- Valve Complete Games Pack $49.99
plenty more..