CEPS, the Cisco Enterprise Print System, is a collection of tools and utilities designed to work together to create a highly scalable, robust printing environment for a medium to large corporation. Open sourced and fully under the GPL license.
This is the home of the CUPS printing system. Version 1.1.15+ has support for CMYK printing.
For everything related to Ghostscript.
Has the Gimp-Print drivers - excellent reproduction on supported ink jets from the Gimp. We'll vouch for the quality and ability to tune the output, EXACTLY, as you wish. Highly recommended for printing high quality photos within Gimp.
GtkPSproc is a front-end for the PSUTILS. PSUTILS is a set of little programs that allows to manage in a lot of ways your PostScript files. GtpPSproc is designed to work from nearly all programs that call LPR, acting as an intermediary between the program and LPR program, but it can work alone too. This is helpful for creating booklets from Postscript printed from Scribus.
Basic but nicely illustrated essay on how offset printing works. Focused on web offset, but relevent also to sheetfed.
A command line tool for imposing pages.
International Paper Sizes: A Compendium of Measurements focuses on papers for printed publications, for desktop/office printers, for business use (including envelopes and business cards), and for imposetters/imagesetters and large-format printers. It records measurements for both standard sizes and commonly used irregular sizes.
Standard paper sizes like ISO A4 are widely used all over the world today. This text explains the ISO 216 paper size system and the ideas behind its design.
Home page for KDE printing, best known for the superb kprinter front end. There also extensive docs on CUPS and print system setups. Recommended for all users, KDE or not. In the downloads is poster - clever utility which is used for printing with tiled output of large prints on inkjets.
Libinklevel is a library for checking the ink level of your printer on a system which runs Linux. It supports printers attached via parallel port or usb. There are graphical fronts ends for Gnome and KDE available too.
Info site for everything printing related on Linux.
A add in to allow posters to be printed on multiple smaller pages. E.g. Print an A1 on A4 pages.
Pstill is a free for non-commercial use comand line ps > pdf converter available for Linux, Solaris and other Unixes.
Offers a wealth of info on Postscript and Ghostscript. Also has excellent section on diagnosing postscript errors and what those cryptic errors mean.