Attached Link: http://www.greatbuildings.com

This is the site for "The Great Buildings" There are quite a few free 3D models of buildings there in .3dmf format. I have converted some of them in the distant past and used them in other 3D apps -- can't say as I remember what I used now. There is a program ($$) I believe it's called PolyTrans that converts just about all 3D formats from one type to another.