Hi Handy,
Really depends on your focus here, time of the year and budget: fun, art, wild side etc. You got your nightclubs as in any other city and restaurants.
Action: all the previous answers have covered the soft drugs entertainment which is pretty unique. Amsterdam is also known for it's legal red light district. There are local politicians that want to close down the district so you may take a look there.
2006 is the Rembrandt year and there are several nice exhibitions in the Van Gogh Museum and other venues.
Biking in Amsterdam, starting spring, is also fun but may be chilly and you need to watch out for the cars.
Food: Eat an indonesian rice dish and cool down with beer. Also try one of the several chocalate boutique stores for good chocolate.
Canal ride may be boring but also easy when you have a hangover and don't like to walk.
Try to visit some smaller museums along the canals, like the rembrand huis, besides the exhibition the interior of the canal houses are impressive.