Just recently, they've found a new brown dwarf, UGPS 0722-05, which appears to be only 9.6 light years from Earth. It's also the coolest brown dwarf ever found, at 400-500K (130-230 degrees Celcius). Considering its dimness and the small patch of sky it was found in, there is a strong possibility of even more (and closer) objects will be found. Given its temperature, they believe it maybe the first example of a T9.9 brown dwarf or might be the first member of a new spectral class.
New Scientist Article
Discovery of a very cool brown dwarf amongst the ten nearest stars to the Solar System