Ten years ago, when I still lived in Amsterdam, I spent most of my Saturdays browsing the stalls on the markets in Amsterdam. One area here, called the Jordaan is one of the oldest and probably one of the most Amsterdammy areas in the Dutch capital. In the early days it was a bit of a slum, but nowadays its residents are a bohemian mix of students, artists and young professional types. The markets are a good reflection of this.
On Saturdays there are three markets that kind of blend into one big one. The Noordermarkt traditionally holds an antique market, but besides the many antique and second hand stalls, you'll also find there is a Boerenmarkt or Farmers market selling things like organic cheeses and bread. One thing you shouldn't miss when you're here is to have a coffee and a slice of apple pie at Winkel, on the corner of the Noordermarkt and Westerstraat. Their apple pie is so good that there's usually a queue to get a table, but it sure is worth the wait.
The entire Lindengracht is also turned into a 1km long market on Saturdays. The Lindengracht is technically not a canal. It used to be, but someone somewhere thought it was a good idea to turn water into land and create some much needed parking spots. Much less pretty, but the good thing is that it can house the Lindengracht market. Here you'll find anything and everything, from Iphone covers to syrup waffles and from plastic teapots to women's underwear. It's worth walking all the way to the Lijnbaansgracht side where you'll find the poffertjes stand. I guarantee you that you'll love these mini-pancakes served with a big blob of butter and powdered sugar.
If a weekend of market shopping is not enough, you could come back on Monday when the Westerstraat market is on. It mainly offers fabrics and cloths, but you'll find the odd fruit and veg stall here as well. The Noordermarkt is also on on Mondays again with lots of antiques and second hand stuff. It's not as busy on these days and maybe not as good for shopping, but a big plus is that the queue for the apple pie at Winkel is considerably shorter. It just depends on where your priorities lie.