Riesling is another white grape that is planted all over the world. It's traditional homeland is in Germany, and the Alsace region of France. It can come in many different styles, including dry, off-dry, sweet, and luscious (that's what you call something when it's the sweetest a wine could possibly get). In Germany they make some outstanding dessert wines from Riesling called Trockenbeerenauslese, which means the grapes were hand picked very late after the sugars have concentrated to a very high degree. Many of these wines are also botrytized, a fascinating process I'll describe in detail later. Riesling has a distinctive aromatic character to it, that you will recognize easily after you've had it a few times.
Riesling's claim to fame is it's ability to ripen very late, even in very cold conditions. In cooler climates, like in Germany and Alsace, Riesling is often not picked until October or early November. There it has flavors of grape and apple, and will have high acidity. Many people enjoy Riesling with food because of this high acidity. In warmer climates like Australia, however, Riesling can often ripen quite early, which can dull its flavor and acidity. Here, Riesling will tend towards more lemon and lime flavors. There are some very nice Rieslings to be found here, but they are all grown in areas closer to the water where the temperatures are much cooler.
In the wine world, Riesling has something of a cult following. It's fruity and flowery aromas are seductive to those that enjoy it. In case you couldn't tell, I'm one of those people! It also has something for everyone, because of the range of sweetness it can offer. But for some reason it never really seems to catch on the way Pinot Noir has since the movie "Sideways." Therefore, it is often very undervalued.
Because of its high acidity, Riesling can age in the bottle very well, especially when it's from Germany or Alsace. The wines can pick up accents of petrol (gas) in the aroma, which sounds disgusting, but it's really not, and it never tastes like gasoline anyway, so don't worry.