The Keukenhof in April and May 

Anne Frank House and the Westerkerk

Canal Boat Tour

Canal Bike (if you are up for some exercise)

Bike Tour or just rent a bike (if you are up for some exercise)

Rijksmuseum

Van Gogh Museum

Heineken Experience

Coffeeshop (if you indulge in other than coffee)

Dam Square

Vondel Park

Floating Flower Market

Antique Tram Tour (summer months)

Leisurely lunch or at least coffee and dessert by a canal.

Aalsmeer Flower Auction

One kilometer long street market on Albert Cuypstraat

Summer concerts in the open air theatre in Vondelpark

Trendy small shops in "The nine streets" ("De negen straatjes")

FEBO - food in the wall.  You pay some euro tokens and out comes a great treat.  You may not be sure what you are eating (the titles are  in Dutch), but it is all delicious.

French Fries with the mildly sweet Mayo.

Museum of S E X - Very entertaining and eductaional, a little humourous too.