Modern Museum- Modern Art. Free entrance.
Natur Historical Museum- History about earth, animals and nature. Not free
Nordic Museum- Nordic History and art. Not sure
Millesgĺrden- Museum for artist Carl Milles, lots of art ( Especially Sculptures). Probably entrance. But alot of it is outside so go in the summer.
Historical Museum- Art, Culture, History. Not sure
Medeteranium Museum- Art from the Mediteraniam and Egypt. Not Sure.
National Musem. Loads of art. Probably the best in Stockholm. Not sure
Nobel Museum. Nobel price winners and history.
Postmuseum- Post, letters and Stamps.
Sea Historical Museum. Ships and History about the sea.
Skansen: It's a big parc just outside of Stockholm, with lots of Animals from all around the world and old traditional houses, the also have free concerts there. Defenitely a must see, but go in the summer. It costs something to enter.
Railway Museum: I used to go there as a kid, It's small but kids loves it. I was free, now I'm not sure.
Stockholm's City Museum: History of Stockholm. Not free, unless you're under 18.
Technical Museum. So much fun, especially for kids, cause there is alot to do and try. Must see. Not sure of the prices.
Vasa Museum. You can see the old Vasa Ship that sank
Very popular museum.
East Asian Museum. China, Japan, India etc. Art and Archeology.
Wine and Alcohol Museum. A pretty good museum too, if you like alcohol.
Now you know what to do in Stockholm, if you ever get there