5thSRD.org – A nicely categorized and easy reference for the SRD 5e.
Matt Colville’s Running the Game – Matt Colville’s series “Runing the game” is a treasure trove of good information for new Dungeon Masters.
Cheap & Effective DM Screen
I wasn’t satisfied with the information on the available DM screens so I made my own. 2 landscape style binders (regular ones could work as well), printed cheat sheets, attach them with a few binder clips and you have a large, cheap and effective DM screen that’s completely customizable with the content you need at a glance. It isn’t going to be winning any beauty contests as is but I’ll take function over form any day.
Polyhedral Dice Set – A set of 7 different colored dice sets for cheap. More dice than you’ll need to get started!
New DM Handbook: Starting Your Adventure – Handy tips for beginning an adventure.
5 Room Dungeon – A guide to building a 5 room dungeon that is simple, effective, and unique.