I got an extra demo disk (#37) from the November issue of Xbox magazine.
Free to the first post or PM (If you live in the US).
Playable demo's include:
OutRun 2 (Xbox Live demo)
Otogi 2
Area 51
Rainbow Six 3: Black Arrow
Kingdom Under Fire
BloodRayne 2
SNK vs. Capcom (SVC Choas)
Fight Club
Download Center includes:
Psi-Ops
Shadow Ops
Silent Hill 4: Track 1
Silent Hill 4: Track 2
And all the other crap that comes on these disks.