LED PR style bulbs (the ones with the flange, not the screw-in kinds) have been around for a while but were expensive, over $20 each for really bright ones. Recently I found inexpensive bulbs for 2-cell and 3-6 cell flashlights that have reasonable luminosity for less than $5 each from Dorcy (#41-1643 and #41-1644). Search the web to get the current best price, they are carried in lots of places.
I bought a bunch of them and put them into every flashlight I have, even the big, heavy ones. They use about 1/4 the power of equivalent incandescent bulbs (PR-2, PR-4, etc) and have a 10,000 lifetime. They also run at full brightness even if the batteries are getting low (a disadvantage if you fail to check your batteries!).
With them I've turned some old, obsolete lightweight incandescent flashlights into perfectly serviceable LED ones.
Actually I normally carry two Photon Freedoms (one white, one red or another night-vision compatible color), but once in a while I want something more powerful.