These links have helped me a lot, and should be bookmarked by any Slacker!

http://www.slackbook.org/ - The official Slackbook - The first place to check for any Slackware Linux related questions. After the manpages, of course ;)

http://slackware.com/lists/ - Slackware mailing lists. Make sure you are on the security and announce mailing lists, else you may not know about important patches being released for Slackware - a big point as Slack doesn't have a package manager that does this for you like other distros.

http://www.slackbuilds.org/ - Slackbuilds can make building programs from source a lot easier, and generate slackware .tgz install packages for you. This means both easy installation and UNinstallation. Reading the scripts can also help you learn how to do it yourself.

http://rlworkman.net/ - Robby Workman's pages - some very useful Slackbuilds and Slack packages available here, not to be forgotten.

http://www.slackware.com/~alien/ - AlienBob's pages - more useful builds and packages, which have saved me from several headaches.

http://slackwiki.org/Main_Page - Slackware Wiki (Unofficial) - No Prizes for guessing what you will find here :)