The Cocktail Party app tells you what you can make from the ingredients you have, and makes tailored recommendations about what to buy next. It's the best $3.99 you'll ever spend on your liquor collection.
We downloaded the app after seeing it as one of the top posts on /r/cocktails, and we've been playing around with it and adding our ingredients to the list. While it's not an all inclusive list of ingredients (missing some creme de ), it's a solid overall app and tosses out some truly spectacular recipes based on what you have in your liquor cabinet. Minor quibbles for an otherwise fantastic application!
JCorduroy, iTunes App Store
Delicious cocktails you can make from stuff you've got around the house.