Here are all the damagebits I found from all the different ways to die in all official maps. I might have missed one or two, but I hope not.
Explosion and resulting pit on payload maps: 0
Lumberyard cliff: 0
Hoodoo cart pit: 0
Hightower cliff: 1
Trains: 1 if touching either gate, 16 if not
Thundermountain cart pit: 8 if you jump in quickly, else 0
Gravity (and most cliffs): 32
Upward cart pit: 32
"Kill" in console: 6144
"Explode" in console: 10304
Drowning: 16384
Sawblades: 65536
Harvest pumpkins: 393280
I'll post a link to my Suicide Notifier plugin that uses these codes as an example once I submit it.
Hope this helps someone!