ATSC - Advanced Television Systems Committee, an international organization establishing broadcasting standards for digital (including high-definition and data broadcasting) television. Provides press releases and many technology papers.
Digital TV - A Cringely Crash Course - An easy to read overview of television, including a brief history and an explanation of the benefits of today's digital broadcasting.
Digital Video Broadcasting (DVB) Project - An international organization partnering with ETSI/CENELEC/EBU for the development of digital television standards for terrestrial, satellite and cable broadcasting. Many fact sheets and a worldwide overview of countries using DVB-T are available.
Dolby TV Audio - Dolby site contains numerous PDF links about Dolby audio technology
How Stuff Works: How Digital Television Works - In-depth unbiased multi-part tutorial explains digital television (DTV). Shows how the worst computer monitors you can buy have more resolution than the best analog TV set.