Puzzle Hunt Calendar
The Puzzle Hunt Calendar is a website that lists puzzle hunts, and is currently the de facto website for most puzzling event notifications. Any hunts, recurring game events and similar are listed on the website, often first announced there.
The website is found at http://puzzlehuntcalendar.com/ and is maintained by Dan Egnor. The website also includes a "Planning Cabal" which helps check for any scheduling conflicts with unannounced hunts.