vanilla extract
Vanilla extract comes from the process of macerating the vanilla beans in alcohol and water. Whatever you do, don't buy the fake vanilla extract! the quality is poor, and thus you will not achieve the desired results in your baking.
The best vanilla, in my opinion comes from Madagascar, an island off the coast of Africa. The harvesting methods gives it its quality.
One thing you should be aware of when purchasing vanilla extract: make sure the label says extract on it, that way you know that it was made with alcohol and water. If it says flavor, then you know that it is not the real thing.
I normally buy my vanilla at Penzey's, I have found that they offer the best quality for the price.