Parapuzosia seppenradensis, biggest known ammonite, diameter 1,80 m
I used to collect rocks, minerals (especially asbestiform minerals), crystals, geodes, and such - but it's such a heavy hobby when you're moving frequently. Still, wouldn't it be fun to have something like this in your den as a conversation piece? Or maybe in the back yard. It's awesome.
Museum not specified; via Minerals and Fossils.
Addendum: Museum found! (Readers of this blog seem to know everything :.)) It's in the foyer of a German natural history museum. And apparently it was the "fossil of the year" in 1998. (auf English)