Here's an at-a-glance guide to who's finished where from all the previous contests, and for the sake of getting meta I've added a ranking system. 1st place gets five points, 2nd gets four, 3rd gets three, 4th gets two and 5th place gets one point. Please bear in mind that there are other ways of ranking the contest winners, this is just the one that seemed simplest to me. A more comprehensive method would take into account the number of contests entered by each person and average their score out (Ildorf, for example, has at the time of writing finished in the top 5 of every contest he's entered, which is a little bit impressive really) but frankly that seemed like far too much work for my liking. If anyone wants to have a go at it themselves though, be my guest.
*NOTE - As of 07/2013, users who were only ever active on the old site and never signed up for this one are marked in grey text.
NOTE 2 - As of 01/2014, due to the amount of users on the list, the text was beginning to get unreadably small. For this reason, the list now shows only users with five points or more (ie. those who have either won a contest or placed in the top four at least twice).
So, here's the leaderboard as it stands after the Album Covers contest:
...And below are all the old ones, for posterity.