There are various artists, called 'Boo' or BOO! :

An Alt Rock band from South Africa, a rap trio from Detroit and a Czech-Austrian alternative rock band Boo (without exclamation mark). Boo is also a ‘monky punk’ band from South-Africa. The album ‘Shooting Star’ is from the South-African band. Boo is also the alias of a promising young MC/producer from Moscow (Russia), who has so far made his name through guest appearance on a smash radio hit “Expensive Love” (“Dorogaya Lubov’”) also featuring Loc (fellow rapper of T.

Read more about Boo on Last.fm.