Click here (and bookmark) this incredibly valuable tool. It's the Swing State Project's sortable calendar of filing deadlines, primary dates, and, where applicable, runoff dates in all fifty states. Very useful - try it! (We'll also permalink it in the right-hand sidebar under "SSP Resources.")
I also wanted to take this opportunity to ask: which states have party conventions instead of or in addition to primaries, and how do they each work? I know, for instance, that Minnesota, Connecticut and Utah all have conventions, but their effects on ballot access differ somewhat from one another. Convention experts, please enlighten us.