StormC - The only currently updated commercial C compiler for the Amiga, from Haage & Partner. - http://www.haage-partner.de/com/storm/sc_e.htm
Amiga Support Network - A forum for developers, testers and user groups to gather, mainly focused on the new Amiga SDK. - http://www.amigadev.net/
DICE C - Source code to version 3.15 DICE C compiler, from Obvious Implementations Corporation. Version 3.2 is apparently still available, commercially. - http://www.obviously.com/dice/
No Amiga To Waste - No Amiga To Waste is aimed at letting users and developers exchange ideas, in order to hopefully minimise wasted development effort. - http://thunderstorms.org/NATW/
Amiga Inform - Homepage of the Amiga port of Inform, a compiler to create text adventures in the Z-Machine format. - http://www.missingpiece.com/inform/amiga.html