Thanks to the hard working Xbox Live Backwards Compatibility team, the already long list of original Xbox titles has expanded just a little bit more, adding close to 40 titles which will now work with the Xbox 360.

December 2006 Back Compat titles added/updated:

Buffy the Vampire Slayer
Burnout 3: Takedown UPDATED
Conker: Live and Reloaded
Dead Or Alive Ultimate
Destroy All Humans!
Dynasty Warriors 4 / Shin Sangokumuso3
Evil Dead: A Fistful of Boomstick
Ex Chaser (Japan Only)
Family Guy
Far Cry: Instincts
Fahrenheit/Indigo Prophecy
I-Ninja
Leisure Suit Larry: Magna *** Laude
Mortal Kombat: Armageddon
MotoGP
Incredibles/ Mr. Incredible (J)
Muzzle Flash (Japan Only)
MX Unleashed
Open Season
Pariah
Plus Plumb 2 (Japan Only)
Psychonauts
Psyvariar2 Extend Edition (Japan Only)
Rainbow Six: Lockdown
Rapala Pro Fishing
Rent-A-Hero No. 1 (Japan Only)
Scarface
Shark Tale
Shenmue II
Soul Calibur 2 North America only
Splinter Cell: Double Agent
Tenerezza (Japan Only)
The SpongeBob SquarePants Movie
Ultimate Spider-Man
Wakeboarding Unleashed: Featuring Sean Murray
Whacked!
Winback 2: Project Poseidon
Xiaolin Showdown

You can view the full list here.

Thanks Major.