My Five Favorite Markets:
1. Borough Market (Southwark): a foodie's dream. Open Thursday through Saturday, this food market -- located near the Globe Theatre -- is a heavenly blend of artisan chocolates, cheeses, breads, juices, wines, vegetables, teas, and basically every other exotic, luxurious, delicious food that you can think of. Stock up on groceries for the week or have lunch on the cheap by filling up on the market's many free samples.
2. Alfies Antique Market (Marylebone): an amazing assortment of vintage clothes, decadent jewelry, fantastic antiques and light fixtures. There is also a charming rooftop restaurant where you can stop in for a quick bite to eat while shopping. It's one of the few indoor markets I've been too, which means that regardless of rain or shine you can go to the market on its days open Tuesday through Saturday.
3. Portobello Road Market (Notting Hill): arguably the most famous market in London. It attracts tons of tourists and locals alike for its mix of costume jewelry, vintage clothing, and local foods. The stalls are open Saturday only, but it's worth it to check out Portobello Road during the week to visit stores like Cath Kidston and All Saints, and vintages shops like Dolly Diamond and One of a Kind.
4. Camden Stables Market (Camden): Camden Market is an umbrella term that covers four different markets and streets of stores open every day. My favorite is the Stables, which are literally old horse stables converted into stalls where you can find alternative and vintage fashions, ethnic foods, vinyl records, screen-printed tee shirts, furniture and global housewares.
5. Spitalfields Market (Spitalfields/near Liverpool St): open five days-a-week, Spitalfields offers vintage clothes, pieces from local designers, jewelry both homemade and antique, and a wide range of old books (I picked up a first edition of A Twist of Lennon here for five pounds!) and comics, pastries, kebabs, fur gilets, leather shoes, manual cameras, and compasses.