Anthony Hawkins' Wine Reference Material - Searchable glossary provides information about hundreds of types of grapes. Also contains vintage charts and tasting note terminology.
Meta Description: [ Strat's Place - Anthony Hawkins - Wine Reference Material ]

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.
Meta Description: [ Learn about wine the visual way. The Wine Grape Varietal Table is a great gift for beginners and experts alike. ]

Enjoying Viognier - Features news and information about Viognier, a wine of the month, and a searchable database of retailers and prices.
Meta Description: [ Enjoying Viognier is a unique website dedicated to just one grape variety and to all those who enjoy the wines produced from it. We want to increase your enjoyment by helping you to discover new and different Viogniers from around the world. ]

Grape Varieties - Information includes wine styles, characteristic flavors, and vinification methods.
Meta Description: [ Twenty-nine major grape varieties are listed so that users can click on any one to read about the grape's colour, flavour, body, and other characteristics. ]

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.

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.