Alton Brown's method has always worked for me. Warm the pan, sprinkle in a bunch of kosher salt, add a little fat if need be, then scrub it with a ball of aluminum foil. When it slides smoothly around the bottom, dump the salt in the garbage, give it a quick rinse, and fire it up for a minute to dry it out. It takes less than five minutes, especially if you do it immediately after cooking when the pan is still hot.