Classic with random room shapes.
I can do a 640x640 map under 2 minutes on an i5 1.2ghz with 4 gigs ram. My dungeon rooms are all done with procedures and my rogue maps do boxes, circles, triangles, diamonds, H's, doughnuts. I wrote this in Java for fun and here are some of the references I used.
Lots of room for improvement obviously, but I don't think I did too bad for my first dive in to map generation. I did start with recursion to generate these maps but they took way too long and ate up a lot of memory. I changed to a different method and avoided recursion. Still it was fun to dabble in recursion for a short time.