Fan Nickname: A small circle of fans gave Doom's... erm... manhood... a nickname, (Doomieconda) and it became a running joke that he has a case of Biggus Dickus.
Not to mention the assorted nicknames for the band members, such as Reesh, Paulchen and Tillies.
Keep Circulating the Tapes: The video of the Live Aus Berlin performance of "Bück dich". Only some VHS tapes had it on there, later tapes and the DVD do not. One suggests looking at YouTube.
The early songs which either evolved into separate works or simply were not put on albums would also count. Ex: "Feuerräder", "Biest", "Jeder Lacht", ect.
Offer Void in Nebraska: Liebe ist für alle da got indexed and the song "Ich tu dir weh" had to be removed from future copies of the album to be sold without age restrictions. However, that's only effective in Switzerland, and Austria. All other countries could buy the uncensored album. Germany's ban was lifted.
Real Life Relative: The extra vocals on "Spieluhr" were performed by Richard's daughter, Khira Li Lindemann.
The whistling on "Roter Sand" and "Liese" was performed by Flake's wife, Jenny Rosemeyer.
What Could Have Been: The album Rosenrot was originally called Reise, Reise Volume Two. Half of it's contents are leftovers from Reise, Reise.
The music video for Sonne was originally about the Hiroshima bombing. The band was watching Snow White while stoned one day, and the rest is history.
In a case of "What Couldn't Have Been". Rammstein might not have been created if not for the premature curtailing of Till's potential Olympic swimming career. This was caused by a combination of a stomach injury and sneaking out and buying porn magazines, getting caught in the act, and getting kicked off the team. This is alluded to on the Völkerball cover: the emblem on it is identical to the 1980 Summer Olympics emblem, the Olympics he would have participated in.