Been a long time since I went to Amsterdam, but the museums are def one of the high points
Van Gogh and Rijksmuseum are definitely worth a visit, if you're into modern art then the Stedelijk Museum as well.
Nemo is also cool, it's a science museum, so it has a lot of interactive exhibits and demonstrations and stuff
There's also a museum of sex which is supposedly pretty interesting, a friend of mine went there and had a pretty good time