There have been many LED instructables, so I will mainly focus on what's different about mine and leave you to fill in the details by reading elsewhere. I won't go into calculating resistor values, series vs. parallel, or things like that. Partially because I did this a while ago and don't remember some of the stuff.
First, the rationale: I don't want lights on my bike because they're theft magnets, are more fragile, and more cumbersome. I want a single battery pack that powers a tail light and one or two headlights, and I want to turn it all on or off with one switch. The backpack is the best way to go for me, since I also like to carry my lock in the backpack anyway and always have it with me.
I used two Luxeon Rebel Stars (145 lumens @ 700mA) for the headlights, and two Luxeon III red-orange side emitters for the tail light. I made a little 555 timer circuit (google it) and encased it in epoxy, and rigged up a switch so that the tail light is always blinking, but the headlights can blink or be solid. Due to my electronics half-assery, the headlights actually blink very slightly when "solid." You can't really tell when riding, though.
I went the resistor route instead of using a buckpuck, which I somewhat regret. A buckpuck is especially cool because you can later upgrade to a Li-ion battery pack (much more convenient to charge, and lighter) and it'll still work the same even though the input voltage is different. And it wastes less juice and thus produces less waste heat.
The switches I used are waterproof E-Switch 100AWSP1's, mouser part # 612-100A-A1422 / manuf. part # 100AWSP1T1B4M2RE.
A good place to go for 555 circuit:
Step 1: Wiring
I thought it would be really cool to make all of the wiring really modular so that I could add/remove the blinky circuit or switches or lights or whatever down the line... but the sheer number of connectors needed ended up being ridiculous and I wouldn't do it that way again. It would be much cleaner and more robust to put the blinky circuit and the circuit to connect the battery/switches/blink all together in one little box, and then just plug the battery and lights and switches into the box.
I also used fairly heavy gauge speaker wire which made it a little more clunky than necessary.
Step 2: Tail Light
I used the lens from a cheapo Bell light and a bunch of heatsinks JB Welded together as the backing. JB Weld conducts heat well but not electricity, so it is perfect for attaching the LEDs and resistors to the heatsinks. I "vented" the light by having some empty wire insulation go through the JB Weld seal as a snorkel of sorts. This way it is rainproof (the ends of the "snorkels" face down) but not airtight. I was worried about air pressure and/or condensation caused by the heat from the LEDs. This may have been an overly paranoid precaution.
Even though the color of the LEDs is called red-orange, it's pretty much red. It's the same color as a car tail light. Red-orange is more visible than "real" red. The two Luxeon IIIs make for quite a bright tail light, although the headlights get all the compliments. On to those...
Step 3: Headlights
The headlights are Luxeon Rebel Stars from http://luxeonstar.com . They say that no lenses are currently designed to work with them, and I have no idea whether you could get some to work well enough. Having these on my backpack straps, the lenses would be really bulky anyway, and I don't have a particular need to see far ahead. If I'm riding under city lights at night then I just care about being seen, and I'm satisfied with how far ahead I can see with them in dark areas. It's pretty much a 180 degree blast of light, though. In the city, the street lights all around in front of me are always blinking along with my lights. They blow away every other bike headlight I've been around, and people are always amazed by them. Sometimes I wonder if they're actually too bright and unfocused, but I've gotten no negative reactions of any kind, except when I accidentally turn them on right in front of someone.
The Rebel Stars I used put out 145 lumens @ 700mA. You can get ones up to 180 lumens @ 700 mA. Compare this to a Luxeon III which is 80 lumens @ 1000mA, or Luxeon K2s putting out 75 Lumens @ 700mA or 130 Lumens @ 1500mA. And you can actually run the Rebels at 1000mA, which could get you up to maybe 200 lumens. As I said in the intro, I don't remember exactly what kind of juice I wired them up for, but I believe it was in the neighborhood of 500mA each.
The headlight on the right was the first, and crappier, iteration. I tried using epoxy and that didn't work so well. The left is how I would do it if I were to make another set of these. They're pretty much completely exposed, but they seem to be ok with that. The actual Rebel LED part has this little clear rubber bubble thing, which is pretty fragile and soon was ripped off of each one. But it didn't noticeably change the optics. JB Weld holds them on and seals off the contacts. For each light, I pressed the spiky sides of two heatsinks into each other, which then gave me these slots that I could run zip ties through to attach them to the backpack straps with.
And that's pretty much it!