The main purpose of this section is to list releases by other bands that Dark Tranquillity members have participated on. For more things that sound like Dark Tranquillity in general, your best bet would probably just be to look up other melodic death metal bands.
Other bands of current members:
Mikael Stanne - Vocals for:
In Flames (1993)
Hammerfall (1993-1996)
Niklas Sundin - Guitar for:
Hammerfall (1993-1995)
Laethora (2005-)
Daniel Antonsson - Guitar for:
Pathos (1995-)
Dimension Zero (2003-)
Soilwork (2006-2008)
Anders Jivarp - Drums for:
In Flames (1994)
Other bands of former members:
Anders Friden - Vocals for:
Ceremonial Oath (1995)
In Flames (1995-)
Passenger (1995-)
Michael Nicklasson - Guitar/Vocals for:
Luciferion (1993-1996, 2000-2003)
Bass for:
Sarcazm (1990-?)
Lavett (2009)
Reborn (?)
Bands/releases featuring Dark Tranquillity members:
In Flames - Lunar Strain (1993) - features Mikael Stanne on Vocals
In Flames - Subterranean EP (1994) - features Anders Jivarp on Drums for half of the tracks
All subsequent In Flames releases feature Anders Friden on Vocals, and some give partial lyrics credit to Niklas Sundin, who translated lyrics from Swedish to English for Friden. Sundin also did a lot of their album art.
Laethora - features Niklas Sundin on Guitar
March of the Parasite (2007)
The Light in Which We All Burn (2010)
Dimension Zero - features Daniel Antonsson on Guitar
This Is Hell (2003)
He Who Shall Not Bleed (2007)
Soilwork - Sworn to a Great Divide (2007) - features Daniel Antonsson on Guitar
Pathos - features Daniel Antonsson on Guitar
Hoverface (1997)
Uni Versus Universe (1998)
Katharsis (2002)
Luciferion - features Michael Nicklasson on Guitar and Vocals
The Demon of '94 (demo 1994)
Demonication (The Manifest) (1994)
The Apostate (2003)
Ceremonial Oath - Carpet (1995) - features Anders Friden on Vocals
Passenger - Passenger (2003) - features Anders Friden on Vocals
Guest appearances of Dark Tranquillity members:
Mikael Stanne (guest vocals):
Nightrage - Frozen (off Descent Into Chaos, 2005)
Scar of the Sun - Ode to a Failure (off A Series of Unfortunate Concurrences EP, 2008)
Solution .45 - Bladed Vaults, On Embered Fields Adust (off For Aeons Past, 2010, also wrote all lyrics)
Niklas Sundin (guest guitar solo):
Sigh - In a Drowse (off Gallows Gallery, 2005)
Martin Brandstrom:
Live keyboards for Tiamat (2009-)
Fredrik Johansson (guest guitar solo):
In Flames - December Flower (off The Jester Race, 1995)
Anders Friden (guest vocals):
Grievance - three tracks off The Phantom Novels (1999)
Caliban - I See The Falling Sky (off The Awakening, 2007)
Nuclear Blast All-Stars: Out of the Dark - Dysfunctional Hours (2007)
Pendulum - Self Versus Self (off Immersion, 2010)