The Pirate Bay allows users to search for and download BitTorrent files (torrents), small files that contain metadata necessary to download the data files from other users for example movies, tv shows, softwares, games... Registration not required.
Torrentz is meta-search engine that combines results from torrent search engines. It's very easy to use, you just have to insert what you want to search for, and it will search for you all torrent links available. Registration not required.
BTJunkie is an advanced torrent search engine. It uses a web crawler to search for torrent files from other torrent sites and store it in its database. It has nearly 4,000,000 active torrents and about 4,200 torrents added daily, making it the largest torrent site indexer on the web.
BTJunkie indexes both private and public trackers using an automatic web crawler that scans the Internet for torrent files. Cookies are used to track what one downloads so that the person doesn't need to register in... Registration not required.