Patrón has a very informative website with lots of information about how they craft their tequilas and beautiful photography. They also run a Margarita of the Year competition that showcases mixologists and their recipes - there's also video of how the winners mixing their creations.
A comprehensive site published by Scarlet and Grover which includes informative educational videos about the state of the industry, tequila recipes, and an extensive database of tequila reviews. They also are the creators of the Tequila Matchmaker app, which is the leading tequila database app which is very useful when shopping for tequila. I recommend you subscribe to their newsletter.
Published by well-known tequila evangelists Alex Prez and Mike Morales, the site is full of video and audio reviews of tequila. The site seems to aimed at generating sponsors for their “Sipping Off the Cuff” series and their “Brands of Promise Tour”, so it’s difficult to search and find content if you are interested in finding reviews of specific tequilas or just general tequila information, plus it has a lot of annoying banners. It’s worthwhile following them on twitter @TequilaAficion as they regularly promote their content and some of it may grab your attention.
This article gives a very easy to follow, and extremely well illustrated, condensed article on how tequila is made. If you have 15 minutes and want to understand the production process from field to bottle, then this is the place site to visit.