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 versions 2.1 (mirror), 0.8
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
Statistics and graphs