Here are some non-random links:

Personal links:

rabenauge my demo group.
hunter a CBM8xxx open source tool by me. It helps to explore the CRTC.
Para’n’Droid open source of an old Android demo. Some parts were created by me.

Commodore PET:

Zimmers File Archives very cool Commodore 8-bit file area.
André’s 8-bit pages much info and documentation about the Commodore PET

C128/C64:

6502.org Commodore documentation and more.
Retro Programming nice German blog about C64 programming.
VICE Emulator for many Commodore platforms.
z64k the currently best C128 emulator. But also for other platforms.

Vectrex:

vide very cool Vectrex stuff e.g. Vectrex-IDE,emulator and much more.

Demoscene:

demoscene.info Infos about demoscene
Computerkunst e.V. based in Berlin
Digitale Kultur e.V. based in Cologne

Various:

hinüber backpacks the best backpacks ever ;)