Google has come to realize that YouTube is becoming a mini music service and has launched a new project called the Music Discovery Project and Playlist Creation Tool.
The tool allows you to enter an artist or band name, and press a big "Disco!" button. The resulting page features a description of the artist or band you chose, with a sample playlist of related tracks pre-populated.
The sound quality of the YouTube videos vary but this is still a great way to gather songs for a party playlists.