I picked up the Nite-Ize L.E.D. Upgrade Combo from Target today ($10), to convert one of my Mini Mag-Lites to an LED bulb. It's not the best conversion kit, but it's relatively inexpensive and locally available. It also includes a replacement tailcap with a switch, which is nice. It was pretty easy to install the tailcap and new bulb(s) and reflector, and so far I'm satisfied with the light it provides.
I also picked up an Inova Microlight (Red LED) ($7) for my keychain. You can find a review here. Oh yeah, Flashlight Reviews.com is a nice source of information on both incandescent and LED flashlights and bulbs.