Smithfields, in the city, is the old meat-market in London. It's one of the oldest markets in London: meat has been bought and sold there for more than 800 years, and it's housed in a fabulous old covered market place, which has been recently refurbished. Because the butchers work all hours, there are 24-hour cafes open, good for a 4 am bacon sandwich after a big night out... (I'm told).
On Charterhouse Road, next to the market, is a great cafe/bar/brunch venue called Smiths of Smithfields (SOS). I had breakfast there before my hair appointment yesterday - delicious, and good coffee. It's apparently quite famous. Cool web-site too.
(image via google)