Designing Markets for Daily Deals.
Yang Cai, Mohammad Mahdian, Aranyak Mehta, and Bo Waggoner. Proceedings of the Ninth Conference on Web and Internet Economics (WINE-13).
Also available on arxiv. Both links are the "full" version.
Useful Tips, Tricks, and Techniques. A list-in-progress I am compiling of some of the most common and useful approximations, inequalities, bounds, proof techniques, etc. for theoretical computer science.