Tarot Supplies:

Tarot Shoppe - books, decks, and more. (Amazon)

Associations and Communities:
Tarot Connection (podcasts) - dedicated to the traditional, historic and modern Tarot.
Aeclectic Tarot - online community and forum.
American Board for Tarot Certification - networt, support, for those who want certification or are Tarot enthusiast
American Tarot Association - courses, seminars, and gatherings (U.S.)
Tarot Certification Board of America - non-profit, standards for professional amateur tarot readers. Seven levels of certification from Apprentice level up to Grandmaster.
The Tarot School - located in New York, certification and degree programs, in person and on line courses available. Host annual Readers Studio, a three-day event held in April.
Tarot Institute - tarot articles, news, free materials, and more.

Tarot Experts:

Rachel Pollack - Bio: One of the World's foremost authorities on the modern interpretation of the Tarot. She is also a poet, an award-winning novelist, and a Tarot card and comic book artist. She has published 12 books on the Tarot, including 78 Degrees of Wisdom (Thorsons, 1998), considered a modern classic and the Bible of Tarot reading.
Tarot Moon (Thrysse) - a true tarot expert she is a Certified Tarot Master and former Secretary of the American Tarot Association. Site contains numerous detailed Tarot spreads, articles, and Tarot deck reviews.

Tarot Resources:

Tarot Garden - collection of popular in-print Tarot decks as well as imported, unusual, hard-to-find, out-of-print, and rare collectible Tarots; features an online searchable database.
Tarot History: the French Marseille Tradition (by Jean-Claude Flornoy) - history, legend, and symbolism of the arcana, divination, the image-makers of the tarot. "This tradition is seven centuries old, and originates in the knowledge, science and art of the men who built the cathedrals. All tarots which are not rooted in this tradition (effectively dead by 1730) can be called "fantasy", and just reflect their authors. Personal creations remain creations which are only personal, however erudite or beautiful."
Tarot Passages (Diane B. Wilkes) - 100s of decks with imagines, reviews, articles, and various tarot spreads.
Tarotpedia - An encyclopedia of tarot contributed to by an online community.
Trionfi - the most comprenhensive history and origin of Tarot.
The Mystic Eye - tarot decks from A to Z, includes pictures.

Tarot Blogs:
78 Notes to Self: A Tarot Journal - Ginny Hunt
All About Tarot - Lyn and Paul (United Kingdom, the ramblings, observations and events of the All About Tarot team.
Wise Tarot Magazine - The first international online magazine dedicated in blog and journal style online to full coverage of the growing Tarot community (estimated at 50 million worldwide). This comprehensive Tarot blog features Tarot Deck and Tarot Book reviews, Tarot Personality Profiles, Detailed Card definitions, and more.

Fun, Interesting, and\or Other Related Sites:

Llewellyn's web tarot and other free fun.
Tarot Jewelry - by Dragonweave.
Tarot Links (Biddy) - huge collection of Tarot related links.