Sweeteners like sugar and syrup are part of the original template for a cocktail (along with spirits and bitters).
When it comes to syrups, the best ones are home-made; we've included instructions for DIYing many of the syrups listed here.
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.