I just did this to the rear of my bike this afternoon, it cost me $3.98 plus a little liquid tape, shrink tube and solder. I didn't do the front because I think the glare on the windshield would be annoying. I'm running stock signals in the stock locations. I used Radio Shack # 276-0084 red LED assemblies these are threaded, have an integrated resistor and require a 13/64 mounting hole. I drilled the white plate around the socket at the 5 o clock position. I tied into the tail light circuit on the hot side and grounded through the turn signal grounds (that way I only had to feed one wire through the stem per side). They work great, they are plenty bright and the signal is easily visible over the LED. I think if I was doing it over I'd have mounted them at 1 o clock, I feel like they'd show up a little better. web page flicker.com
If you try this but can't find the same LEDs I used just be sure the ones you buy have a luminous intensity of 50 mcd or better, also the viewing angle of these is 100 degrees, I'm not sure how important that spec is but it's the widest field of view I could find, seemed like a good idea to me.
