http://linuxprinting.org A central compendium of information on printing in Linux. Download official and unofficial open source drivers. Read the recommendations in the Suggested Printer List when you're in the market for a new printer. Ask questions in the forums.
http://h10018.www1.hp.com/wwsolutions/linux/products/printing_imaging Hewlett Packard's Linux driver efforts.
http://www.tldp.org/HOWTO/Printing-HOWTO From the page, "A collection of information on how to generate, preview, print and fax anything under GNU/Linux."
http://www.cups.org The place to keep up with the Common Unix Printing System.
http://www.pwg.org/ipp The IETF Printer Working Group's page on the Internet Printing Protocol (IPP), used by CUPS. Very technical, but a good FAQ.
http://www.ghostscript.com The Ghostscript news and community page. New release announcements and a community component based on "diary entries."
http://www.cs.wisc.edu/~ghost The Ghostscript home page.
http://www.adobe.com/products/acrobat Learn more about Acrobat and PDF from the official site. You can also download the free Reader here.
http://solutions.brother.com/linux/en_us The Brother Linux support and driver status page.