Tools Tutorial has moved!
The tools-related content of this tutorial has been moved to the official Mod DB tools page.
Modeling / Skinning Resources
Don't feel like you have the creativity to come up with your own modelling and skinning, or are having a really tough time find a modeller and skinner? Try out these two sites, which give you both for free!
AddonDB - Moddb.com
The brand new network site from the creators of ModDB, AddonDB is your one-stop shop for all of the addons you could ever think of. From character models, weapon models, and maps, to sounds, skins, and tools, this site is the only resource you're ever going to need.
FPSBanana - Fpsbanana.com
Perhaps the biggest customization site solely dedicated to FPS games on the Internet today, FPSBanana provides a wide assortment of tweaks and tools to help you in your endeavor to make your mod.
Advertisement / Recruiting
Need help for your mod or just wanted to spread the word? Here are some pretty good sites that are frequented by a lot of gamers and modders. You can usually try the forums themselves, and get feedback or help. Of course, it's always recommended to try Moddb first for help requests and advertisement. If you aren't getting heard, here are some interesting sites I visit myself:
Planet Sites - Gamespy.com
You can basically find a site for any game that can be modded through this network. Join their forums and start pimping your mod, or try to get hosted by one of the most popular sites on the Internet and gain coverage from the widely-read GameSpy front page and newsletter.
FileFront Network - Gamefront.com
Much like the GameSpy network, FileFront hosts a number of sites solely dedicated a single game, so you can browse through there and even get your files hosted on their site for fantastic exposure. On the main page, just click one of the games under "Browse Popular Games", then visit their community page.
MODSonline.com - Modsonline.com
A huge site dedicated solely to mods, much like Mod DB itself, but on a smaller scale.
Still having a trivial time trying to figure out what you're supposed to do in a certain situation? Here's a batch of sites that can be really useful when the going gets tough in your modding endeavors. You can also use the sites under Advertisement / Recruiting for backup.
ModDB Tutorial Database - Moddb.com
Containing an extensive amount of tutorials covering almost every facet of modding development, the ModDB Tutorial Database is a highly recommended area to begin your search for additional help. And please, if you happen to benefit from these documents, give back to the community by submitting your own to help keep that section of the site growing.
3dBuzz - 3dbuzz.com
One of the best resources available on the Internet, this site is jam-packed with plenty of tutorials. One of the best hallmarks is that it also provides video tutorials to help you with everything from modeling and mapping to lighting and texturing. Also, for a small fee, you can participate in online-only classrooms where instructors teach you the different fundamentals of modeling programs. This is definitely one site you want to keep in your bookmarks.
Frequently Asked Questions about Mod Programming - Planethalflife.com
This is a good place for beginners to get started creating Half-Life specific mods. This FAQ covers all the basics.
Wavelength: Your Editing Resource - Thewavelength.net
Wavelength has information on coding, creating models, and even embedding your own sounds within a mod. Not only does the site have a variety of helpful tutorials, it also includes a forum where mod makers can exchange ideas and tips.
Wikipedia - En.wikipedia.org
Where can you find all of your information anywhere else except on Wikipedia? This great site is busting at the seams with content dedicated to helping you with any modding question you may have. It even contains pages detailing the programs I have mentioned above, in case you weren't aware of them in the first place.
Interlopers.net - Interlopers.net
A site containing a helpful community and plenty of tutorials to sift through, Interlopers is a great site if you're looking for some help on your mod. It's also a good place to advertise your mod to the community and gain some much-needed support.
Valve Editing Resource Center (VERC) - Collective.valve-erc.com
Formerly the Half-Life ERC, the Valve ERC has grown to encompass all of Valve's products. The site contains user forums, tutorials, and lots of technical details for advanced mod creators.
Valve Developer Wiki - Developer.valvesoftware.com
This is Valve's official developer resource for Source-based developing, It includes the old Source SDK docs and a continually growing amount of user-added developing resources.
This is THE place to look when developing on Source.