I just discovered UnSpun, an Amazon project (still in Beta) which allows you to “Find the Best, Find the Worst, Vote Your Opinion, Create Your Own Lists”.
To put it simple, you can create a new list (i.e., best bra color… anyway, that one is already in the top ten at the moment ), and make people vote, or search for an existing list and rank other users’ opinions, or just add yours if it is not present in the list so far. You can use your existing Amazon account, if you have one.
Both fun and useful (I suspect the “Best Xmas present for girlfriend/wife” list to show up in the top 3 in a couple of months ).