Camden Lock Market was established in the 70s as a temporary market on a site which was intended to have a road built over it shortly afterwards. The road never came, however, and the market has been there ever since. The markets cover a vast range of tat, from second hand clothes, to art, food, glowsticks, furniture and many other things which you don't really need.
Whilst the nearby Hawley Arms has already recovered from the 2008 fire, the Canal Market *edit* largely reopened this weekend *edit*. The rest of the markets, with the exception of the area being redeveloped in the Stables Market, escaped the fire and you can still easily while away a couple of hours there, and if you get bored of the smelly goths, it's only a short walk to Regents Park.
For more information, visit http://www.camdenmarkets.org/.
*this may not be true, but it certainly seems like it