Game Master's Day is one of those great ideas that never quite seems to get enough love. It's held on March 4th ("March Fourth for Game Master's Day"), which means this is the first year I've actually had a post up about it on the day it was happening.
The idea is that today's the day you can heft a glass of Mountain Dew and thank your Game Master for a job well done ... and maybe buy him or her a little something.
Like Valentine's Day, GM's Day primary proponent has been gaming companies and stores who traditionally offer discounts (sometimes significant discounts) on their products. This year the Biggest GM's Day sale I could find is at RPGNow.com, which has PDF books on sale from dozens of publishers. Of these, Adamant's having the sale that's got me most excited: all of their books are going for $1, and a number of these are ones I've had my eye on for a while. These include Mars: The Roleplaying Game of Planetary Romance,their Star System line of generic PDFs for science fiction rpgs, and Thrilling Tales, a pulp take on the d20 rule set.
Other good deals include Rogue Game's Thousand Suns scifi RPG (only $7.49 for the PDF) and RPG Object's entire line (including Darwin's World, Blood and Space 2) is 25% off. I'm sure there's plenty of other great stuff out there -- my primary interest these days is in science fiction RPGs, since I'm running Star Wars, but even casually browsing through the site I saw a ton of fantasy and horror stuff.
All in all, I think the sale's a great way to show appreciation for the creative engines that keep the hobby going, and a great excuse to get yourself (or your GM) and not feel too guilty about the money you spent.