I don’t include grids on my microdungeons because I want to leave details like that up to the GM. A microdungeon map isn’t a square-by-square representation, it’s a guide. Think of it as a quick sketch of the dungeon, or the hand-drawn map you might find on the Orc chieftain. It represents the layout, but not the proportions. That way each GM is free to size the rooms in a way that fits the encounter.
But I do admire a nice grid map. There are a lot of good map products out there, but personally I’ve been spoiled by John Harper’s gorgeous DIY maps. He used these when we first tried out 4th Edition D&D, and it remains one of the most memorable games I’ve ever played in. His tutorial is very easy to follow, though you probably want basic to moderate Photoshop skills.
The blurred-out backgrounds are a very nice touch (virtually the entire short campaign took place on vertiginously high towers and buildings). As I recall, the example map in his post was a particularly rough fight with some darkness-producing teleporting badasses who almost had us fleeing half way through the fight (we persevered, however, saving the plane from Vecan’s graps. Again.)