I heart allrecipes.com and I have for awhile now. The interface is great, allowing users to easily change proportions, print out recipe cards in a variety of sizes, and generally customize the experience as needed.
But today I discovered Cookthink.com, and well, wow. This site is cool. It allows you to search for recipes based on your cravings. So, for example, you can search by ingredient, dish, cusine or even mood.
A search for "yogurt" and "soulful" returned a recipe for White Gazpacho with Mint & Apple. A search for "uplifting" "Mexican" "chocolate" returned a recipe for a Flourless Chocolate Flour-Basil Torte.
It's by no means perfect, but as the data base grows based on user input, it can only get better. Plus the concept is great. It's metadata put to good use!