Even I Know that's impossible to Link all the good websites...... I've tried to post some good one.....

http://sourceforge.net/ --> portal dedicated to the OpenSource

Packets / updatings:
http://www.debian.org/distrib/packages
http://www.rpm.org
http://rpmfind.net --> all the packets (rpm) possible and imaginable!!
http://freshrpms.net
http://shrike.freshrpms.net --> RPM for Redhat 9
http://rpm.pbone.net
http://www.linuxpackages.net --> all u need for Slackware

Window manager:
http://fluxbox.sourceforge.net
http://blackboxwm.sourceforge.net
http://www.kde.org
http://www.gnome.org

Is your modem compatible with linux?
http://pctelcompdb.sourceforge.net

Documentation:
http://linuxdocs.org
http://www.gnutenberg.org

Web engines:
http://www.google.com/linux

official sites of the various distributions:

http://www.debian.org/
http://www.knoppix.com
http://www.mandrakelinux.com
http://www.mklinux.org
http://www.redhat.com
http://www.slackware.com
http://www.suse.com

server side:
http://www.apache.org
http://www.samba.org
http://www.wu-ftpd.net --> ftp server
http://www.proftpd.linux.co.uk --> another ftp server

do u want to connect yourself from remote to your pc/server:
you can use telnet (not too much sure)
ssh (very surer)
: http://www.ssh.org (default on the commercial versions of linux but absent in the world win )

http://linuxiso.com/ --> all the distributions for moderate prices