I use a relatively cheap ReddyHeater, plumbed into the gas line for the house. Works great for me, but I just have a two car. No venting, really no smell. Life is good...
Got a bit dusty over the summer, but here it is.
Gah. Still an annoyingly large picture, I'll just link it.
http://www.photobucket.com/albums/09...ach/Heater.jpg
I'm no expert on the subject, though.