Amsterdam in two words: (The) Cock Ring
Ignore everything that Ritournelle wrote... he has no idea what he's talking about (although id agree to rent a bike)
dont waste your with the Rijks (State) or Van Gogh musuem, unless you are actually interested in art, and even then, good luck enjoying it when its sardine-style viewing over the summer.
If anything, hit up the Anne Frank Huis along the beautiful Prinsengracht (Princes Canal). Go to the Hidden Church Musueum, or the Verzetsmuseum (Dutch Resistance Museum)... the zoo is cool, the canal tours are fair... get lost in the Jardin district... eat at an Indonesian restaurant, chill at the Spuistraat square... go to the Pijp district for the really cool Albert Cuyp market... take a tour of the nearby Heinken Brewery, which is super fun but get there early to minimize line time.
As for coffeeshops, definitely DO NOT go to La Canna.... its a shit-hole tourist rip off right on the main shopping street. It's one redeeming feature is a view from the second floor onto the pedestrian street... excellent people watching. Otherwise, Amneisa, Blue Bird, Grey Area, La Tertulia, and various others should be pretty good for smoke. It its shrooms your after, most smart shops sell the similar Mexican, Hawaiian, and Uruguayan strains... they will explain the difference. I would dose and then take a bus out to Amsterdamse Bos (that's the forrest west of the city) with plenty of room to trip.
All the gay night life is not on one street, but there are a few areas that are concentrated. Like I said above, the Cock Ring is an interesting experience otherwise check out April's, Exit, and De Trut.
Any more questions? PM me.
Not nearly as knowledgeable on Prague though there is an interesting museum on Communism there... the gay clubs are fair, at best... not like the Bel Ami models you were hoping for.