This may already have a topic of its own, so feel free to relocate it if needed.
The VersaLux ULM is what I'd consider the "Swiss Army Knife" of LEDs, it can run from 2.2 VDC to 13.8, has ten white Nichia LEDs, and is as about "plug and play" as I've ever seen. I got two of them a while ago, and have had more fun just trying out different whacky ideas and experiments with them.
Sure, they aren't cheap ($49.99 ea )but they solve all the problems of building boards, regulators, calculating resistors, etc. Even a simple, crude but very useable flashlite can be made with one and a 9V battery. A simple headlite? One of these, some double sided sticky tape or velcro, a Radio Shack 4 AA cell holder with switch, and a
sweatband or some such stretchy thing to fit around your noggin. The applications are endless...
The site points to some interesting projects and ideas to try out.
/ed brown in NH [img]images/icons/cool.gif[/img]