Cabernet Sauvignon - One of the components of French Bordeaux, it is also a major grape in the most popularly drunk American red wines. Prestige and/or quality are not always equal to popularity.) Cabernet Sauvignon contains a lot of tannins that lead to the long aged, "better" red wines. Depending on where it is grown it may smell of cassis and black currants or black cherry and red currants. Bell peppers, asparagus, and rhubarb are common tasting notes for cabernet produced from grapes that are not quite ripe.
Barbera - A major Italian variety with a "tarry" smell and medium body.
Cabernet Franc - Also a component of Bordeaux, a little is often blended with Cabernet Sauvignon to add bouquet.
Gamay - Produces a fruity wine such as French Beaujolais. (The California Gamay Beaujolais is not the same grape, but makes a wine that comes close.)
Grenache - Often used to make rose wine, it is a component of French Chateauneuf-du-Pape, Cotes du Rhone and most other appellations from the south of France. There are also many tasty grenache-based wines from Spain (where it is called garnacha) and from California.
Merlot - One of the major components of most French Bordeaux, also with less tannin that makes for a smoother characteristic in the wine. Alone (or practically alone), it makes another of the more popular U.S. wines. Though it is like Cabernet, it is usually "rounder". It is often blended with Cabernet Sauvignon.
Nebbiolo - Can be found in California, but is really a grape of the Piedmont area of Northern Italy. Found in Barbaresco and Barolo wines, which can be aged with great success.
True Syrah - a relative of Durif from the Rhone in France (and a major variety in its own right).
Petite Sirah - a variety grown relatively widely in California and said to be genetically the same as the obscure French Durif variety.
Pinot Noir - The only grape in the famous French Red Burgundy appellations of the Cotes de Beaune, Cotes de Nuit and Cote d'or.. Some U.S. winemakers will make Pinot Noir "in the French style".
Zinfandel - Mostly from California, it has a great deal of fruit like characteristics. Some young Zinfandels are also "spicy." Good red Zinfandel is often a bargain in restaurants, being less expensive than other wines, but still very drinkable. A decent White Zinfandel can make a nice "picnic wine".