The Alte Nationalgalerie ("old national galerie", en.wikipedia.org/wiki/Alte_Nationalgalerie) is one of those "you have to have visited" musea, housing a little bit of everything.
The Berggruen-Picasso Museum is a collection of privately held art, made publically accessible. For those interesting in who Berggruen was, feel free to read en.wikipedia.org/wiki/Heinz_Berggruen
The Bode Museum in Berlin (http://en.wikipedia.org/wiki/Bode_museum) is one of those musea you just go see at least once.
All manner of cars. Because there's a lot of cars on this planet, let alone throughout history.
Photographs taken primarily for their composition in terms of lines, contrast, or other scene interplay.
the Gemäldegalerie in Berlin (http://en.wikipedia.org/wiki/Gem%C3%A4ldegalerie,_Berlin) is home to mostly middeaval art, including some rather spectacular pieces
Berlin has this wonderfully cozy little museum for musical instruments. Of course, it doesn't cover the range of all possible instruments, but it's still very much worth while dropping by.
I didn't really like the Pergamon in Berlin, but then you should make up your own mind about it I suppose.
The Art Institute of Chicago is one of those places you kind of have to visit. It's not the British Museum, but then that comparison is weird anyway.
The BlackHawk museum is pretty much the museum equivalent of a "hole in the wall", tucked away in a (to be fair, very pretty) mall in Danville, California. However, if you do find it... well, to quote a kid walking around with their dad "why is the museum not packed with people? This place is amazing!".
Tucked away in the middle of nowhere, an hour outside of Fresno, the Clarks own a large orchard. And as collectors of Japanese art their collection became large enough to make it worth erecting a centre for art. Next to their house. Which is a Japanese manor complete with meticulous Japanese garden. It's... very special. If you're ever at the Minneapolis Institute of Art, and looking at the Japanese art: most of that was donated by the Clarks.