http://www.htpcnews.com - You'll find plenty of hardware and software reviews here, along with an excellent and active support forum. This was one of the first web-sites I started visiting when I decided to get into HTPCs.

SnapStream Support Forums - If you're looking for support specifically for BeyondTV, this is the place to go. They also have a Knowledge Base which has proved to be helpful on more than one occasion. It hosts excellent articles about dealing with capture card issues and controlling your set-top box.

Frey Technologies Support Forums - If you're looking for support specifically for SageTV, this is the website to visit. If you decide to buy or at least try SageTV, you're going to want to visit the Customizations Sub-Forum. Here you'll find all of the cool add-ons for SageTV that can adapt its look and functionality.

http://www.mythtv.org - If you decide to try out MythTV, you'll undoubtedly spend a lot of time here. Since MythTV is the hardest HTPC application (of the four we tested) to configure, there's a lot of documentation on the subject.

http://www.mythtvtalk.com - One of the main support forums on the internet for MythTV. If you encounter a problem you may want to search and post here. It's available in four different languages.

Fedora Myth(TV)ology - The excellent how-to that I followed to configure my test MythTV box. It utilizes the user-friendly Fedora Core distribution of Linux. It also has additional information on remote controls and high definition.

http://www.avsforum.com - The AV Science Forum is where thousands of AV geeks lurk. You'll be able to find information on HTPCs and any other topic pertaining to Audio/Video equipment that you can think of.

Windows XP Media Center 2005 Home Page - This link will bring you to Microsoft's product page. There is some decent information here, including a few flash demos of the application.

http://www.xpmce.com - The Windows Media Center portal! There are decent FAQs here and a knowledge base. Their forums are also really busy.

http://www.thegreenbutton.com - The premier Windows Media Center Community Forum.

http://www.hauppauge.com - If you're looking for a new capture card, this should be your first stop. They appear to be the industry leaders.

SilverStone Technologies - Manufacturer of HTPC Cases. They currently have approximately 16 models available.

Ahanix Incorporated - Another large HTPC Case Manufacturer. They have approximately 6 high-quality, aluminum units available.

http://www.usbuirt.com - If you plan on using an HTPC with your cable or satellite set-top box, you'll want to pick up a USB-UIRT.

Zap2it Labs - A free service that you can sign up for to obtain TV listings for SageTV and MythTV. They may periodically send you a survey to fill out, and that's all that's required to retain this free service.

http://www.tivo.com - If you don't feel like spending the time and money investing in a HTPC, you may want to take the easy way out and acquire a TiVo. Don't be ashamed if that's your ultimate decision. :-)

http://www.doom9.org - Doom 9 is the definitive resource for DVD Backups. Their forums also contain a wealth of valuable information.

Build Your Own PVR - BYOPVR is a solid resource for those of you looking to put together your own HTPC/PVR Box.

If there are any quality links that I've missed, please let me know via email.