Python scripting for computational science - Hans Petter Langtangen
high quality textbook

Syntactic Theory: A Formal Introduction, 2nd Edition - Sag, Wasow and Bender
an OK textbook

Operating systems - a systematic view - Davis and Rajkumar
OK for beginners

Learning GNU emacs - Debra Cameron et al
the ultimate textbook

Innføring i datakommunikasjon - Øyvind Hallsteinsen; Bjørn Klefstad; Olav Skundberg; m.fl.
It's actually possible to write good Norwegian computer books

C Programming Language - Brian Kernighan and Dennis Ritchie
Love or hate

Programming Perl - Larry Wall, Tom Christiansen & Jon Orwant
The ultimate perl book