Though not as big as the flea market in Bürkliplatz, Flohmarkt Kanzlei has the advantage of being open every Saturday year round, regardless, so they say, of the weather. A couple of food vendors are also on hand to offer sustenance to shoppers, in including heisse Maroni (hot chestnuts) in the winter. On the first Saturday of every month, it's also a good stop for a cheap(ish) haircut.
Kanzleistrasse 56, Zürich, Switzerland