There are at least 6 artists with this name:

1) Ra is an American rock band named after the the Egyptian sun god. The band has been around since the 1990s, but did not actually evolve into what it is today until 2002. The current line-up includes Sahaj Ticotin (vocals, guitar), Andy Ryan (drums), Ben Carroll (guitar), and PJ Farley (bass). Their music is described as "exotic yet familiar, heavy yet funky, direct yet sophisticated, sensual yet soulful, unrelenting yet cathartic".

The band released their first full-length album entitled "From One" in October, 2002, containing songs from their demo album "One" and the two radio tracks "Do You Call My Name" and "Rectifier". In June, 2005, Ra released the album "Duality" featuring the original lineup. Before the CD's release, drummer Skoota Warner left the band, and did not accompany them on their April / May 2005 tour. The replacement drummer was current band member, Andy Ryan.

In 2006 Ra released their live album titled RAW on Cement Shoes Records. With the release of RAW, Ra heading out on an extensive US tour called Congress of Corruption as one of the main acts.

Their lastest album titled "Black Sun" was released on Septemeber 23, 2008.

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2) RA was a dark metal/ambient project hailing from Romania, brainchild of Andrei Rusu, also known as Vlad Dracul of Agathodaimon fame. They have released two albums, "Geniu pustiu" (Hollow Genius - 1998) and "Sinnocence" (2002). One of the most notable collaborators within the project was Dan Byron, a guest of Agathodaimon, who later went to sing in Kumm, Urma and Byron.
The project is currently on hold. New demo music is available on the official MySpace page: TribalDome

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3) Ra is an IDM artist fron France named Raoul Sinier. His profile has been moved to http://www.last.fm/music/Raoul+Sinier

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4) Ra is a Norwegian psychedelic trance group. Ra was first founded in 1994 by Christer Borge-Lunde, also of Dimension 5, and Lars W.Lind. In 1998 they went their separate ways and Christer Borge-Lunde continued Ra primarily as a solo project. In 1998 Ra was signed with Blue Moon Productions UK and the first single Azure Child was released. In 1999 and 2000 Christer Borge-Lunde was working with Blue Moon Thailand and collaborated with Charlie Clarke which contributed on the album "To Sirius". The album was first released in Thailand in 2000 and later re-released world wide in 2001 by the German label Velvet/GTN.
In 2006 he joined Suntrip Records, releasing tracks on the compilations "Twist Dreams" (2007) and "Opus Iridium" (2008).
Ra's 2nd full length album "9th" was released on Suntrip Records in May 2008.

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5) Ra is a Norwegian jazz band. Winner of Jazzintro 2000.
Ronny Andreassen (reeds), Morten Qvenild (Fender Rhodes), Ole Jørn Myklebust (trumpet), Kjetil Lunde (guitar), Karl-Erik Rønsen (bass), Erlend Lygren (drums), Stig Værnes (drums) og Andreas Veire (sound)

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6) RA is a Finnish Pharaoh-theme heavy rock band, and all the members are born in 1995. Their debut album Punainen Virta was released 25.2. 2009. Their lyrics are in Finnish.