oh man, i could go on forever...but here's a couple tips
rent a bike, but make sure it's a discreet that doesn't scream TOURIST... i think Mike's Bikes on Kerkstraat (also a gay street) has some decent ones. pay attention to the flow of bike traffic at the beginning. you should be able to get the hang of it pretty quickly. you CANNOT pass up this experience if you are in a'dam.
if you happen to be partying all night as the sun is rising, i suggest a walk around the Jordaan neighborhood... it will be desolate, beautiful and amazing.
there's a gay sex show called Why Not Blue Boy on Spuistraat (also an amazing street for cafes, restaurants, coffeeshops, shopping). it's not as good as you might think, but still novel.
go to the top of the westerkerk church... an amazing view from up there.
buy some shrooms from the Magic Mushroom Gallery and then jump on the 168 bus (or maybe it was 186, not sure) from Dam square all the way to the Bas forrest and trip the fuck out... it's huge and you'll get lost, but it's not that big, so just keep walking straight and eventually you'll get out and figure a way to get home. just make sure it's a pleasant day and you bring enough water and food with you.
as for coffeeshops, everyone has their favorite... i'd suggest just walking around and peaking your head into whichever one catches your interest and seeing if it is worth stopping for a spliff. im partial to Amnesia on the Herengracht (small, comfortable, board games available to play, bongs available for use) and La Tertulia on Prisengracht which makes amazing flavorful shakes and has a few seats on the patio to watch the world go buy on the canal.
Soho is a good gay bar to start the night. then head to Exit next door for a pretty raucous club atmosphere.
if you're into art, obviously van gogh and rijksmuseum. there's also a really interesting history museum called the Dutch Resistance museum, which explains how the dutch resisted nazi occupation.
the canal tours are cheesy, but it's the best way to view the city from the canals unless you have a local friend with a boat.
i could go on and on... so if you have any questions, just let me know