The Ardent Epicure

Agave nectar is a natural sweetener produced from several varieties of the agave plant (blue, green, grey, rainbow, salmiana, and thorny agave), a dry-weather succulent plant grown predominantly in Mexico, but also in some parts of the U.S. and South America. 
The juices from the agave are extracted from the plant, then filtered and heated, causing the liquids to form into a sugary syrup.  This syrup is sold as a commercial sweetener, and can be used in place of other such sweeteners, such as honey and high fructose corn syrup.
Benefits
There are several benefits of using agave nectar over other types of commercial sweeteners.  First of all, it is all-natural, and conforms to strict vegan dieting.  In addition, it is very sweet, and can be used to impart a sweetness that may surpass that of sugar or honey.  Also, this product is often found in organic form, which imparts health and environmental benefits.  Plus, agave nectar is a bit thinner than honey, and dissolves more easily than honey or sugar, making it easier to incorporate into liquids.  Also, unlike honey, agave syrup never crystallizes, and thus will never get hard or creamy.
Types
There are four primary types of agave nectar:
Light Agave Nectar - a mild form of the sweetener, with a more delicate taste and less overpowering sweet nature.
Amber Agave Nectar - a darker, more powerful sweetener, this type can be used when a bit more sugary flavor is needed.
Dark Agave Nectar - the darkest version, with a much stronger, more intensely-sweet flavor, often used in dishes whether the other ingredients will hold up against its powerful taste, such as desserts.
Raw Agave Nectar - similar to the light version of the sweetener, but produced at a lower, carefully-controlled heat, so as not to compromise the original makeup of the product.
Flavored Versions - agave nectar is often sold with flavorings, such as vanilla or hazelnut, and can be used in a manner similar to other sugar- or corn syrup-based flavored syrups available.
Organic Versions - agave nectar is often found in organic form, indicating an extraction from totally natural, pesticide-free plants.
Uses
Agave nectar is used in many of the same ways as sugar or honey or corn syrup can be used.  It can be used to sweeten baked goods and other desserts, as a sweetener for savory dishes, added to drinks, or poured straight onto foods that are typically augmented by a sweet syrup.  Basically, this can be substituted in much any situation where another sweetener may have been used originally.
Food Tip
Try adding light agave nectar to your iced tea or coffee.  It will sweeten much like honey, but will be easier to pour (without heating), and will dissolve much more easily.  Also, try pouring amber or dark agave nectar right onto your pancakes or waffles, in place of pancake syrup.