I've had several people ask me for more information about agave in recent months. For a great overview about agave, I recommend reading Debra Lynn Dadd's write up on it here.
Agave is one of my favorite natural sweeteners because it tastes very much like sugar in recipes. It is a liquid, so it does behave a bit differently than granulated sugar. I usually use 3/4 c. agave for every 1 c. sugar in a recipe. Sometimes I'll go as low as 1/2 c. agave per 1 c. sugar, but I tend to prefer things less sweet.
I also like agave because it doesn't spike insulin the way refined sugars do.
As for where to get agave, you can find it at health food stores, but it's expensive. The cheapest way we have found to buy it is to order a case of it from Amazon. We usually buy Madhava Raw Agave Nectar. You can also order in bulk from Agavebythecase. On that site you enter in the products you are interested in buying and they e-mail you a quote for how much it would cost, shipping included.
At this time, according to Debra Lynn Dadd, Mexico is the only country that produces agave nectar (some have asked if it's possible to find agave produced in the U.S.).