I use these in my darkroom and haven't had any problems with Forte or Ilford paper fogging (10 minute test). They are very bright and one bar of lights was enough for me. Robert, I stll have another bar I can send you if you'd like to give it a shot (and see how bright they are).
I soldered mine (with some heatshrink tubing on the outside) to a variable output power supply from Radio Shack and run them at 9v just to be on the safe side (12v just seems SO bright!).
edit: I have some from the same place Lee Gebhardt bought his from. If you search Apug there is a post or two about this.
Let's see what I've got in the magic trash can for Mateo!
Any electronics shop should have leds suitable for your use. Ignore the 15mcd variants but anything between 500mcd and perhaps 2000mcd will be useable. I don't recommend the luxeon style leds as they'll be too bright. As previously mentioned the ones used for show replacement in cars work well but you'll have to reduce the voltage to lower the current and hence light output unless you have a big darkroom. Maybe buy a few different single ones to try - they're at most only a dollar or thereabouts each and in a darkened room they're bright enough.
I use the Luxeon LED. You'll only need the one - as Roger says, they are *bright*. A simple power MOSFET, 3 resistors and a potentiometer cct will provide a continuous dimmer control, or just use one current limiting resistor and make a shade to adjust the brightness. I made mine so I can plug in external LED heads, but that's probably overkill (and after 6 months, I still haven't gotten around to actually making a remote head - I just plug the LED soldered onto a DC power plug into the remote socket)...
I bought a couple of the red LED bulbs for sale on the APUG classifieds just to check them out. I have not officially tsted them yet for fogging but no apparent problems. They are very bright and only cost about $15 each.
I have not tried. I've heard the shape of the bulb may be critical to getting even illumination, and the shape of the LED bulb would surely be different from what the enlarger was designed for. Also, incandesent bulbs have a continuous light spectrum, so small dips and bumps in the spectral curves of multigrade papers or multigrade filters won't matter too much. On the other hand LEDs only have a few narrow lines in their color spectrum; if these spots happen to land on a "bad spot" of the spectrum of the filter or paper, it could be hard to get the contrast you want.