For those of you who have used Roll20 to play online with friends, but don't do more than a quick "/roll d20" and you want to try out 1st edition AD&D, method three presents a challenge.
Roll each stat in order. Roll 3d6 for each stat. Six times. Pick the best. Go to the next stat.
To make this easy, you can use the following:
/roll {3d6,3d6,3d6,3d6,3d6,3d6}kh1
This translates to "roll six sets of 3d6, keep the highest one"