If you do not have the budget for diamonds, and you want to have a heavenly pleasure, then you hit chocolate. My good old favorite is Leonidas, which is an affordable option that can be found all around Antwerp. A bit more expensive giant of the chocolate world is Godiva, and it can be found basically in every neighborhood in Antwerp. There are also some bakeries and chocolateries producing excellent bonbons, and I want this to be the surprise of your trip, so no clues.
If you like chocolate in other forms than bonbons or pralines, you can stop by at Guylian, located at Komedieplaats 15. Komedieplaats is a very elegant location--a luxury shopping street. You can watch the ladies in smart clothes around Hermés and Cartier while having a chocolate shake with passion fruit, or you can have a chocolate dip of the current season's fruit. Even though a bit pricey, it is a stop for something different.
For budget minds, the best place to taste chocolate in a different form is the street; there are waffle booths on many main streets. Try a warm waffle with chocolate on a cold winter day, and you will feel like the luckiest person on earth. And if you ever see a girl messing with the chocolate all over her face and, eventually, clothes in front of one of these booths, that could be me.