NOTE: These links are somewhat historic. Some may need updating.
Eclipse IDE for C/C++, Java, and other languages
FreePV open source panorama viewer
IrfanView image management software: Free software for photo sorting and some simple editing. Currently only available for Windows.
The open source alternative to Google Maps, Tom Tom and other map and navigation software providers.
Processing programming language and environment
Sourcery CodeBench Lite Edition. Formerly called CodeSourcery G++ GNU Toolchain for ARM Processors.
WinAVR GCC for Windows for AVR ATMega processors