I got this one, rated 525CFM:
http://www.homedepot.com/h_d1/N-5yc1...&storeId=10051
I had to build a custom insert for my window, with a square hole to mount the fan in. I also drilled a hole for the propane hose to go through to the tank outside. I disconnect everything, remove the fan from the window and take the hose inside after each session. I was actually surprised how powerful this little plastic fan is. Very pleased.
This one looks promising for a larger room:
http://www.homedepot.com/webapp/wcs/...5673%2d%5f%2dN