Jesse Rutherford (@BentTronics) gave us an in-depth look at the 555 timer IC (wiki).
Jesse runs Bent-tronics.com and wrote The Ultimate Beginner's Guide to the 555 Timer (Amazon).
Some great 555 projects:
555 Decimal Adding Machine
555 found in a drill trigger speed controller as seen on the Ben Heck Show
555 found inside a solar charger controller, video by Julian Ilett