There are at least seven bands named 'Sin', 'SIN', or 'S.I.N.':

1. Filipino Technical Death Metal Band SiN started in 2001. MySpace | Metal Archives Page

The band consists of:

Charles Daza - Vocals
Alvin Quinones - Bass
Rommel Vasquez - Guitars
Gilchrist Tan - Guitars
Macoy Manuel - Drums

They have also released an EP entitled "Pilgrimage" which was released back in 2004. They recently shared the stage with Shadows Fall in the PULP Summer Slam 2008 event.

Many who claim to have listened to the band, they are the Philippines' answer to the band Meshuggah from Sweden.

2. French industrial group (Frank Renov, Damien Barquero, Vincent Brunello)
http://www.digital-sin.net
Label: Recall Records (http://www.recallrecords.com/usa/index.php).
Releases: Noisy Pipes Lovely Noises (1998), Painful Reconstructed (?), Errare Digital Est (2002), Reconstructed Singles (2003)

3. Vienna-based group (Mona Moore, Andy Orel and Richard Dorfmeister)
http://www.sin.at
Label: Abuse Industries
Releases: Where Shall I Turn? (EP vinyl 1990), Where Shall I Turn? (MCD 1994), Where Shall I Turn? - Remixed (vinyl 1994), The Man Who Hates Himself (MCD 1995), The Man Who Hates Himself - Remixed (vinyl 1995), SIN EP (CD 1996), Insinuation (CD 1998), Sin Remixed (CD 1999), And I Sigh (MCD 2001), And I Sigh (12" 2001), Kissing (CD 2001), So Sad (CD 2003), So Sad remixed (12" 2004), Absinth (Double CD 2005)

4. Solo American hip-hop artist (Pierre "Sin" Ferrand)
http://www.myspace.com/soulstudents
Releases: Welcome to the Show (2005)
Japanese band
Store Appearing To Carry Their Releases: http://www.cdjapan.co.jp/detailview.html?KEY=HFCA-1104
Releases: Sin (with first track NIGHT TOO BRIGHT), I Want You Back (2000), ...

5. Turkish group
Some promotional tracks available here on Last.fm.

6. American industrial group ("Chris and Robert")
http://www.worldofsin.org (currently dead, archive.org lists it through sometime in 2004: http://web.archive.org/web/*/http://www.worldofsin.org/sin.html)
Tracks available on the Interbreeding III and IV compilations from BLC Productions (http://www.blcmusic.com).

7. Solo Canadian Rapper Philip "SIN" Philippi
Born in Belgrade, Serbia and moved to Canada as a refugee in 1994.
As a rapper he is highly regarded by most Serbian immigrants in Northern America but not recognized as much back "home" in Serbia for his dislike of a certain ethnic group.
Currently CEO of his self-started label, Sizzerb ent.
Albums:
Opium Garden (2006?)
myspace.com/sizzerbsin