What are some common seedless varieties of grapes?

Seedless varieties include the following:

• Thompson seedless grapes represent more than a third of the table grapes now grown in California. Light green and oval in appearance, they are juicy, crisp, and sweet.

• Black Beauty, often called the Beauty, is the only seedless black variety. Its flavor resembles that of Concord grapes, spicy and sweet.

• Flame seedless grapes are a blend of the Thompson, Cardinal, and a few other varieties. They have grown rapidly in popularity to become the second most popular table grape after the Thompson seedless. They are round and deep red, with a sweet-tart flavor and a pleasant crunch.

• Tokay (Flame Tokay) is a sweeter version of the Flame seedless grape. Its fruit is large and elongated with orange-red color and crisp texture.

• Perlette is a round crisp green grape with a frosty white bloom on its surface. It is the first grape of the California season and one of the hardiest varieties.

• Ruby seedless are deep red, oval grapes with a sweet flavor and juicy flesh.

• Black Corinth, often marketed as the Champagne grape, is a small, purple grape with a delicious wine-like sweetness and crunchy texture. It is usually available at gourmet markets when fresh but is more common in dried form as the Zante currant. 

• Superior is a fairly recent variety but has become popular for its sweet flavor and distinctive crunch. This grape is bright green  and elongated.

Source(s):
Whole Foods "Guide to Fruits"
Tonytantillo.com "Fruits: Grapes"