2 days in amsterdam and 2 days in brusssels

Jumping in before all the Brussels haters on this board do... Depends on what your interests in Brussels are. Definitely see the Grand Place and the historic district around (but don't eat in the rue des Bouchers, it's tourist trap central). If you are a gallery/museum enthusiast I definitely recommend the National Museum of Ancient and Modern Art, the Musical Instrument Museum, and if you can read French or Dutch reasonably the National Comic Strip Centre (less rewarding for anglophone-only). If you really are an art fan also try the smaller but still interesting Ixelles art museum in the suburbs, and if you are into early twentieth-century art I strongly recommend the Victor Horta museum house and a walk around the other art nouveau town houses in the St Gilles area. If you or anyone you're travelling with is into transport the Autoworld museum and the City Transport museum with its vintage tram lines. Also there are some spectacular dinosaur skeletons at the Natural History Museum. If the weather is nice it's pleasant to have a wander round the park at Laeken and see the Atomium (don't bother going inside).

Rather than repeat Phillip's recommendations, and re-type what I wrote on another similar reply, see the thread "Belgium Bound" under the "To the West" section.

Museum Willet-Holthuysen is brilliant! If you drink gin, jenever tasting is interesting.
S

Go to Brugge!