Anthony Hawkins' Wine Reference Material: Searchable glossary provides information about hundreds of types of grapes. Also contains vintage charts and tasting note terminology.
De Long's Wine Grape Varietal Table: Offers information about 144 varieties organized in an interactive table. Also sells a print version of the table.
Enjoying Viognier: Features news and information about Viognier, a wine of the month, and a searchable database of retailers and prices.
Grape Varieties: Information includes wine styles, characteristic flavors, and vinification methods.
P.S. I Love You: Industry organization dedicated to promoting the Petite Sirah grape. Includes a history of Petite Sirah, articles, a list of members, and recipes of suggested food pairings.
Pinotage Association: Association promoting South Africa's Pinotage. Contains a history of the grape, winemaking information, and a producer list.
Pinotage Club: Cyber club for fans of the Pinotage grape of South Africa. Includes information about the grape, a newsletter, links, and membership details.
The Zin Zealot: Focuses on Sonoma County Zinfandel. Includes links to information about the grape, tasting notes, and a list of wineries.
Vitis International Variety Catalogue: Searchable database with very technical information and some pictures.
Wine and Juice Grape Varieties: Information about varieties suited for cool climates.
Zinfandel Advocates and Producers: Non-profit organization dedicated to promoting Zinfandel. Contains information about the grape, membership details, and a list of events.
ZOW - Zinfandel on the Web: Contains tasting notes and links to Zinfandel-producing wineries.