Mixologist is probably the most well-rounded of all the mixology apps in our list. You get all the usual recipes, search by ingredients, random selection and so on, but also bartender tips and terminology, and a bar/liquor store locator which is particularly handy if you're out of town.
My favorite feature is the "Browse all" category, which usually is just a huge meaningless list, but in this app you get the title of the cocktail with the main ingredients underneath, so you know before you tap whether this drink is for you or not. It even has a glass icon to the left of each entry so you know what kind of cocktail it is -- long glass, tumbler, shot, champagne flute etc.
Unbelievably for just 99 cents you get access to thousands of recipes, which is enough to keep you going through many parties to come. I also like the units option to look at either imperial or metric measurements so it really should keep everyone happy.
The only small issue with this app is that if you search on ingredients for something you have in your cabinet like "brandy", you'll also get results for cherry brandy and apricot brandy as well, which started to get annoying. Overall though, it's a minor issue and the results will still offer you loads of options for whatever bottles you do have to hand.