Half-Life 1 Series
http://web.archive.org/web/20030201222819/http://www.half-life.com/
http://web.archive.org/web/20010610155729/http://www.sierrastudios.com/games/half-life/
http://web.archive.org/web/20001007044643/http://www.halflife.net/index.html
http://web.archive.org/web/19991103141955/http://www.halflife.org/
http://web.archive.org/web/19990117031133/http://halflife.gamedesign.net/
http://web.archive.org/web/20010603090406/http://sierrastudios.com/games/half-life-dreamcast/
http://web.archive.org/web/20010610212406/http://sierrastudios.com/games/half-life-playstation2/
http://web.archive.org/web/20010801145335/http://sierrastudios.com/games/hl-blueshift/
http://web.archive.org/web/20011005171907/http://www.sierrastudios.com/games/opposingforce/

Half-Life 2 Series
http://web.archive.org/web/20040526025124/http://half-life2.com/
http://web.archive.org/web/20050228224243/http://www.half-life2.com/
http://web.archive.org/web/20060701042408/http://half-life2.com/
http://web.archive.org/web/20060409033145/http://ep1.half-life2.com/
http://orange.half-life2.com/

Team-Fortress: Classic
http://web.archive.org/web/20001110104800/http://www.teamfortressclassic.com/
http://web.archive.org/web/19990508064141/http://www.sierrastudios.com/games/tfclassic/
http://web.archive.org/web/20011019141400/http://sierrastudios.com/games/tf1.5/

Team-Fortress 2: Brotherhood Of Arms
http://web.archive.org/web/19991003221720/http://www.sierrastudios.com/games/teamfortress/
http://web.archive.org/web/20011128174209/http://teamfortress2.sierra.com/
http://web.archive.org/web/20010202032800/http://team-fortress2.com/
http://web.archive.org/web/19990218071258/http://www.teamfortress.com/
http://web.archive.org/web/20050410074308/http://tf2.sierra.com/
http://web.archive.org/web/20000815205819/http://planetfortress.com/
https://web.archive.org/web/20100323134718/http://www.dhlp.de/tf2.php3

Gunman Chronicles
http://web.archive.org/web/20001109050100/http://sierrastudios.com/games/gunman/
http://web.archive.org/web/20010718141958/http://www.3dactionplanet.com/gunman/info/index.shtml
https://web.archive.org/web/20000229173232/http://gunman.valveworld.com/
https://web.archive.org/web/19981111183641/http://gunman.telefragged.com/
http://web.archive.org/web/20000510111012/http://gunman.telefragged.com/
http://web.archive.org/web/19980218103719/http://planetquake.com/gunman/
http://web.archive.org/web/20001203125900/http://www.gunmancentral.com/

Valve's Website (Obviously the individual pages vary over the years, but this design stuck around for a long time)
http://web.archive.org/web/19980216132230/http://valvesoftware.com/

Fan Websites (Chronological)
https://web.archive.org/web/19971221175843/http://half-life.warzone.com/