I have no interest in obtaining and maintaining a large collection of mariachi links, so instead I have provided a short list of some of the larger and more established mariachi sites on the web. In them you will find much more comprehensive collections of links, and I expect all of these sites to exist for some time.
Puro Mariachi -- the largest collection of mariachi links I have found, fairly comprehensive.
ElMariachi.com -- has a large collection of lyrics to mariachi songs and other good information.
Mariachi Education Resources -- a good source, includes the Mariachi Publishing Company.
Mariachi Connection -- a store in San Antonio that sells a lot of mariachi materials, including music, trajes and instruments.
DrMariachi.com -- ask Dr. Mariachi anything you would like to know about mariachi music
Viva El Mariachi -- lots of great info
Mentioned in Virtuoso Mariachi:
Los Changuitos Feos -- my first mariachi!