Links
Hovels is a great source for hand-painted 6-25mm resin
buildings.

Total Battle Miniatures makes a wonderful line of buildings in
an assortment of scales, and they are available "painted."

Gamecraft Miniatures has the largest selection of Middle
Eastern Buildings in 6-20mm.  Allen's service is also top notch.

Elhiem Miniatures sells beautifully sculpted WWII and
modern day miniatures in 20mm.

Timecast Models produces a beautiful line of 6mm resin
buildings suitable for WWII.