jdrakeh
Front Range Warlock
Demon Driven to the Maw is a one-shot that I've had a lot of fun with (I've played it in OD&D, B/X, and Six-Hack).
The hardcover book, which includes all of those and more, is also excellent and an extremely easy book to grab when you find out that two of your five players aren't coming this evening or someone still has their old character sheet but hasn't played in eight years or any number of similar situations.There's three different books of One Shot Wonders available on DDB; they are each really well designed for a mini-session, around two hours. There's enough content to run the adventure, along with maps, but each is basic enough to make them easy to tailor to a specific group and setting, if you want. So if you use DDB, a book of those might be ideal (they're inexpensive, and you're supporting a 3PP).