From what I've seen this decade here are my favorites:
1. The Ring
2. 28 Days Later
3. Paranormal Activity
4. Cloverfield
5. Dawn of the Dead
6. The Ruins
7. Ju-On: The Grudge
8. Pulse
9. The Mist
10. Quarantine (haven't seen the original film REC but I hear it's superior)
Honorable Mentions:
28 Weeks Later
Slither
Dark Water (original Japanese version)
Dead and Breakfast
Prey
Land of the Dead
The Descent
The Others
Black Sheep