Treasure was formed in 1992 by a group of game developers who left Konami. Before leaving, they were responsible for developing the Contra series and Castlevania among others. Their first release was Gunstar Heroes in 1993. Below is a list of all their releases with publishers and release dates sorted by platform.
Arcade:
- Radiant Silvergun
- Treasure 5/1998 Japan (Sega ST-V Titan)
- Ikaruga
- Treasure 12/20/2001 Japan (Sega Naomi)
Dreamcast:
- Bakuretsu Muteki Bangaioh (Bangai-O in US and Europe)
- ESP 12/9/1999 Japan
- Swing! 10/20/2000 Europe
- Electro Source 3/21/2001 US
- Ikaruga
- ESP 9/5/2002 Japan
Game Boy Advance:
- Tiny Toon Adventures: Buster's Bad Dream
- Swing! 7/5/2002 Europe
- Conspiracy TBA US
- Hajime no Ippo: The Fighting
- ESP 12/12/2002 Japan
GameCube:
- Ikaruga
- Infogrames 1/16/2003 Japan
- Infogrames 4/16/2003 US
- Infogrames TBA Europe
Mega Drive/Genesis:
- Gunstar Heroes
- Sega 9/10/1993 US and JP
- McDonald's Treasureland Adventure
- Sega 9/23/1993 Japan
- Sega 12/1993 US
- Dynamite Headdy
- Sega 8/5/1994 Japan
- Sega 6/14/1994 US
- Yuu Yuu Hakusho
- Sega 9/30/1994 Japan
- Alien Soldier
- Sega 2/24/1995 Japan
- Light Crusader
- Sega 5/26/1995 US and JP
Nintendo 64:
- Bakuretsu Muteki Bangaio
- ESP 9/3/1999 Japan
- Yuke Yuke! Trouble Makers (Mischief Makers in US)
- Enix 6/27/1997 Japan
- Nintendo 9/30/1997 US
- Tsumi to Batsu: Chikyu no Keishousha (Sin and Punishment: Successor to the Earth)
- Nintendo 11/21/2000 Japan
PlayStation:
- Rakugaki Showtime
- Enix 7/29/1999 Japan
- Silhouette Mirage
- ESP 7/23/1998 Japan
- Working Designs 1/6/2000 US
PlayStation 2:
- Silpheed: The Lost Planet
- Capcom 9/21/2000 Japan
(re-released 9/26/2002)
- Working Designs 5/1/2001 US
- Swing! 5/11/2001 Europe
(re-released 7/19/2002)
- Stretch Panic (Freak Out in Europe, Hippa Linda in Japan)
- Swing! 7/27/2001 Europe
- Conspiracy 8/30/2001 US
- Kadokawa Shoten 12/6/2001 Japan
- Tiny Toons Adventures: Defenders of the Looniverse
- Conspiracy TBA US
- Infogrames TBA Europe
Saturn:
- Guardian Heroes
- Sega of Japan 1/26/1996 Japan
- Sega 4/24/1996 US
- Silhouette Mirage
- ESP 9/11/1997 Japan
(re-release 12/10/1998)
- Radiant Silvergun
- ESP 7/23/1998 Japan
There is no doubt that there were numerous cancelled titles as well. One high profile project they had was Magical Hearts: The GunBeat (aka Gunbeat.) It was a racing/shooting game being developed for Sega's Naomi arcade hardware. The project was officially cancelled 5/22/2000.
I had difficulty confirming the existence of some games, the Game Gear versions of Dynamite Headdy and Gunstar Heroes in particular. I'm not sure if these were developed by Treasure or re-coded by another company. I also believe that the Yuu Yuu Hakusho series for SNES was not developed by Treasure. If you believe that any of this information is inaccurate, please /msg me.
I've redone the formatting and decided to keep all the publishers hardlinked for readability. Feedback on this is appreciated.
Primary sources:ign.com, gamefaqs.com, http://www.mrmonkeyman.com/treasure/