Update: February 18th - Chrysalis Day and Discord Day added.
For the sake of simplicity and since we get a lot of questions about this, I've thrown together a calendar showing off each specific pony celebration day. Save it, use it, prepare with it, and be ready to celebrate the glories of each main cartoon horse on the show! Or dragon in Spike's case.
And below the break, get quick archives to all the posts we have celebrated for each of these characters in their previous days, because sometimes it's fun to just go look at a wall of posts celebrating the best of a specific pony on ANY day!