If I forgot to add someone to this list please let me know.

Main developer, improvements, bug fixing
Davide Anastasia (Lead Project Mantainer & Mac OS X support) <davideanastasia@users.sourceforge.net>
Franco Comida <fcomida@sourceforge.net>
Daniel Kaneider (windows setup, head of i18n efforts)
Bruce Guenter

Contributors:
Christian Raue (German Translator)

Mandus (Norwegian translator)
Nicholas Phillips (MTB alignment code)
Mustafa GÜNAY (Turkish translator)
Douglas E. Warner (fc6 packager and bug reports)
Jan Gemela (Cezk translator)
Peter Gaal (Hungarian translator)
Ignacy Gawedzki (tiff ldr bugfixes and suggestion)
Bertrand Petit (FreeBSD patch)
Sloan Poe (found and fixed bug regarding legacy actions signal)
Alexandre Prokoudine (gui improvements, desktop integration)
Arne Hagenah (various suggestions)
Frank Boehme (various suggestions)
Erik Ouchterlony
Antoine Latter
Markus Schmaus (found and fixed bug in Debevec and Robertson02)

Original author:
Giuseppe Rota <grota@sourceforge.net>