Everybody knows the Magnum's book called Contact sheets. (If you don't have it, buy it immediately. And if you want to know why it's so important, read that. Pour ceux qui ne lisent que le français, contentez-vous de ça.)
One of the most difficult and interesting time for photographer is the editing. I had a lot of discussions with friends on this subject. (Friends from Marseille at first, but also friends from my collective or passionated discussions in Hyderabad with Vinod Babu and Swarat Gosh.)
But I didn't find any group dedicated to discussions on editing on Flickr. So I created one on contact sheets for share on editing. You can join us at Cooking sheets.