This 68W behemoth from TCP, Inc. , rated at 4200 lumens, claims to provide the same amount of light as a 300W incandescent, yet can be installed in any fixture which can safely accept a 75W incandescent.
Energy Federation Incorporated and Conservation Mart both want $24.50 for it, but Home Depot had them for $14.50. Lighting Supply Co. has them for $24, in both 2700K and 5100K versions. (The other vendors are all selling the 2700K version.)
One big detail is that the bulb itself is rather large: it's nearly 10 inches long and about 4 inches in diameter, so it won't physically fit in a lot of fixtures. Still, although I didn't pick one up yesterday (I wanted to do some comparison shopping first), I want one. I'm sure I can find someplace to put it.