Just posting random stuff in here based what on I see as good enough starting info or links to code and such, don't come whining to me if you wonder into a gray zone. :P

Basic no frills but deep emulator

http://en.wikipedia.org/wiki/NO$GBA

Not been able to track down the dev kit tielf yet
[url]http://linuxdevcenter.com/pub/a/linux/2003/11/06/devkit_advance.html[/url]

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tons and files and some info
[url]http://darkfader.net/gba/main.html[/url]
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This is a devkit for home brewing

[url]http://devkitpro.org/[/url]
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Another homebew site with source files.
[url]http://www.gbadev.org/[/url]

Add anything you got to the list, trying to build a simple but comprehensive base for users to jump in and start deving.