It looks like Modern Warfare 2 and Left 4 Dead 2 might be fighting it out for top PC first person shooter of the year in terms of sales. This week's top 10 best selling PC games (in terms of revenue) on Steam has Infinity Ward's military shooter on top with Valve's zombie shooter down to the number two slot.

Valve's holiday sales last week helped to make this week's list have a little more variety:

1. Modern Warfare 2 - Infinity Ward/Activision
2. Left 4 Dead 2 - Valve
3. THQ Complete Pack - THQ
4. Mirror's Edge - EA
5. Borderlands - Gearbox Software/2K Games
6. Battlefield 2: Complete Collection - Rocksteady/Eidos
7. Dragon Age: Origins - BioWare/EA
8. Left 4 Dead - Valve
9. The Chronicles of Riddick: Assault on Dark Athena - Starbreeze/Atari
10. Dragon Age: Origins Deluxe Edition - BioWare/EA