Okay, so this will take me a few to finish, but here we go
So in every version of MC pre-1.7.2, Items had an ID code.
(found here http://minecraft-ids.grahamedgecombe.com/ )
Typically everyone who wrote mods reserved 0-256 for Mojangg ID's
Forge and FTB/ Tekkit reservered 0-2000, but quite a few authors dipped down into the 1500 range.
Here is a quick forge list
http://www.minecraftforge.net/forum/index.php/topic,638.0.html?PHPSESSID=6W8fH4rWrh2QnXNPyRgcS2