Torrent is one of the best peer-to-peer protocols. It is distributed, fast, and open. One of the things that are missing or, rather, underdeveloped is search. Searching is difficult due to the decentralised nature of the protocol. TorrentSpy.com helps to cure the problem by indexing many large Torrent collections.
Update (February 5th, 2016) : TorrentSpy.com has been shut down by the US court, apparently.