Castle, as in that ABC show that stars Nathan Fillion and the (quite) hot Stana Katic.
Below is the official but very short opening of Castle.
Below is a very cool homemade remix of the song.
No official information is available for this song, however, I’ll go out on a limb and say that it was done by a composer named Robert Duncan, simply because he is credited in the show’s IMDb page. It makes sense though, because Mr. Duncan in a known composer for television and film, and composed music for shows like Buffy the Vampire Slayer and The Unit.