GSnap - With GSnap you can get an auto-tune effect.
Spotify - Map shows when two people play same song at same time
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
SoundCloud - Enjoy music & follow favourite artists
CrispyTuner - Fully featured vocal tuning suite.
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm