There are lots of Half-Life sites out there. Many are mod sites, others are news and info sites, and some are resource sites. Here are a few of the better ones.

• HLGaming.com
  You're looking at it. Naturally, it's the best out there :P
• The SnarkPit
  The biggest and, editing/community site for Half-Life. Filled with smart and well-known people, and with lots of great mapping tutorials. It also has a great many map reviews.

• The Valve Editing Resource Center
  The official Valve site for Half-Life. No longer updated, but has a good deal of great info. It has now morphed into...
• The VERC Collective
  The official Valve community site, run by Autolycus, the Valve Community Liason. Filled with lots of really, really deep stuff on the inricacies of Half-Life editing, and also includes the official game entity list (woot!) and a massive forum.
• The Wavelength
  Filled with tutorials covering every single aspect of Half-Life editing. It's currently being redesigned, but the older version with all of its content intact is still viewable.
• The Handy Vandal's Almanac
  If you can't find something on the Almanac, it probably doesn't exist :). The largest collection of editing links for Half-Life anywhere. Even Valve promotes it, so it must be good.
• Spirit of Half-Life
  Respect the L-Man. Laurie Cheers, author of the most useful programming toolkit for Half-Life - Spirit - has his site here. If you make mods, you want this kit. Don't deny it, I can feel your desire from here.

• The Half-Life IRC Tool
  Is a powerful Half-Life launching utility that is written entirely in mIRC script. It contains a built-in favorites list that allows you to add, remove, query, and connect to servers, without ever leaving mIRC. It has support for the remote console protocol, which allows for remote administration of Half-Life servers. Provided that you have the rcon password to a server, you can execute any server console command, without even joining a game. HLIT also includes a highly customizable messaging system, triggered status replies, and automatic IRC nickname changing. HLIT even has the ability to query the WON master servers.
• Banzai Maps
  It's primarily a site where you can download the latest custom TFC maps by Kami, CaL, Mercior, Madjai, Sui and Fisheye.
• Jobabob's Maps
  A mapper for both Counterstrike and Team Fortress 1.5 and have only officially released 1 'serious' map so far (The_Valley), the others (such as the 2001 series) being skills maps.

• Global Assault
  A massive collection of multiplayer maps. With reviews too!
• Hot Death Diner
  A great map reviewing site, and runs mapping competitions as well. Prizes!
• HL Atlas
  A comprehensive map reviewing site