Wiki
Here are some Debian related diagrams and sketches, please add more:
Maintainer scripts 1 (src)2 (src)
Debian development process (src)
Ubuntu & Debian development (src)
Debian package breakdown
Debian build system
Debian & neuroscience
Understanding Debian infographic
Release timeline, General timeline
Debian package cycle
Flow of autotools artefacts (src)
apt state files (src 1 2)
maintainence problems & Debian
Relationships between apt, aptitude, dpkg etc
Package diagram
Suites diagram
Diagram of the NEW process
Diagram of the upload process
dgit design process
The Debian DNS universe
Statistics and graphs