There are three artists with the name Dark Horizon:

1) Dark Horizon is an Italian symphonic power metal band based near Piacenza.

2) Dark Horizon is a Gothic Metal band from the United Kingdom.
Dark Horizon's official website
MySpace profile.

3) Dark Horizon is a hard rock band from Costa Mesa, California.
MySpace profile.

4) Dark Horizon is an electro‑goth collaborative project from London, England.
MySpace profile.