I got great thick dark smoke from using sprites and the smoke imagery in the maya "gifts" folder in the Maya program directory
Make sure to use raytraced lights for best results.
And because they are pre-rendered images, it renders REAL fast too!
Check the docs for how to set-up sprites, and also check the readme in the gifts/smoke folder
Good luck!
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS
izzylong.com