There are 7 bands known under this name:

1) Horizon were an Indianapolis straight edge band, who released a record called "Where The Blind Lead The Blind" on Catalyst records.

2) Horizon were an indie/pop rock Christian band from Sydney, Australia. They had promising songs but broke up in 2008.

3) Horizon (Norway): Horizon is a soft rock band formed in 2005. their music is an alternative soft rock\funk.
Band Members:
Adrian Kristiansen: Vocal
Audun Efftevåg: Guitar
Daniel Abboud: Guitar
Daniel Heinesen: Bass
Johannes F. Alfheim: Drums

4) Horizon is also an more familiar band from USA, the soundtracks from Last.Fm is theirs.

5) Horizon is also a German Melodic Power/Prog Metal band with two albums the 2002 The Sky's The Limit and 2004's Worlds Apart

6) Horizon was also a dutch doom/death metal band.

7) Youtube user Hanyuudesu, a song writer and singer who often does covers of Vocaloid songs. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.