LED Blacklights
Light Emitting Diodes (LEDs) that emit black light are now available. They seem to be good sources of strong, pure black light. They are also tiny, and use little power.
There has been a lot of interest in UV "black light" LEDs, largely kicked off by the glowing creature eyes that Jim Kadel sells through Haunt Master Products. Jim gets points for offering the first commercial haunt products using black light LEDs and has suggested many haunt uses for this technology.
Black Light Leds are available in many different forms, normally either as a keychain torch, which is very handy if you are interested in Antique glass such as depression glass / Uranium glass.
Due to cheap fakes coming in from china, this type of black light is handy when checking out green glass to verify if it is simply JUST green glass of is in fact uranium glass.
Flourescent blacklights
The best black light for all-around haunt use is a fluorescent black light. These resemble the regular white fluorescent lights, found in offices and stores, except that they use a special lamp that emits black light. The lamps used for black light effects have several modifications from the standard white fluorescent lamps.
These are generally fairly cheap and are usually ready to turn on.
Incandescent black lights
Incandescent black lights do emit some black light, however they also put out quite a bit of visible purple light. Opinions differ on the use of incandescent blacklight and claim that the purple visible light detracts from the glow of the fluorescent object they are trying to illuminate. Others say that it adds a more somber and scary look.
Like all incandescent lights, incandescent black lights do put out a lot of heat, that's because they are visible-light bulbs, with the internal coating trapping most of the visible light.