For those who like to start new worlds, a new mobile app sanctioned by Mojang has been released. It contains a list of world seeds with short descriptions of the seeds and ratings. To quote Lydia (The Weekly Chunk & Snapshot 12w32a
App Store - Seeds For Minecraft
Seeds are curated and rated. You will even see photos and descriptions of each seed. Not only can you check out seeds in the PC version, but there are also ratings and suggestions for seeds on the Pocket Edition and Xbox version!
It is also available for Android and the Kindle Fire but Mojang hasn't given a link.