How do I find out the most popular tv series, movies, music, games and anime?

An easy answer is simply to look at the amount of people downloading torrents!

As of 2009-09-01, the current ones are:

TV SERIES (http://www.torrentz.com/verifiedP?q=tv)

MOVIES (http://www.torrentz.com/verifiedP?q=movie)

MUSIC (http://www.torrentz.com/verifiedP?q=music)

GAMES (http://www.torrentz.com/verifiedP?q=games)

ANIME (http://www.torrentz.com/verifiedP?q=anime)