Got some stuff sitting in your pantry that's been there a little too long? The expiration date is just around the corner, and you want to cook something new that doesn't require going to the store? Lucky for you there's SuperCook, a service that lets you figure out things to eat based on what you've got. Unlike some other services that do this, SuperCook separates the wheat from the chaff (poor choice of phrases I know) by showing you the recipes you can make with what's in your kitchen, and those that require a few extra items to match up with their original recipe.
To add items to your virtual kitchen, you can simply start typing names in. SuperCook's got a suggest-as-you-type feature that makes it pretty simple to add a lot of items quickly like you would with tags on Flickr. Once they've been added they stay there until you remove them, meaning you can come back to the site later on and make a few adjustments to get updated recipes. This is especially helpful with spices, as a few added or missing ones can change hundreds of recipes at a time. Users who sign up can get their kitchens permanently saved, along with the option to bookmark recipes they like.
In addition to its recipe recommendation by ingredient service, SuperCook gives you Amazon.com-like recommendations for other ingredients you should pick up based on what you've got laying about. What's interesting here is that these recommended ingredients change based on what type of dish you're working on, as the service lets you cycle between entrees, starters, and deserts. It's also a super-simple way to stock up your virtual kitchen without having to type what's there.
I like this service already, but it's in a very crowded space. Other sites like Allrecipes, RecipeMatcher, Google Base (recipe version), and Snacksby have been around a little longer and offer similar functionality that most folks will be happy with. I still prefer SuperCook's virtual kitchen idea and ingredient recommendations, which I think make it more useful than most.