There are loads of these on Barchester's 'Suppliers' page but if you know of other good ones then post the link here to share with everyone. Don't forget to write a few words on why you are including the link.

This I found via MRF

Welcome to Battlezone Miniatures - Battlezone Miniatures

while it is mainly for wargammers, it has trees, paints, all sorts of goodies.

Rustystumps.com

 US company dealing in H0, 0 and S scales.
 Great range of doors and windows for scratchbuilding, and white metal and resin castings of cupboards, workbenches, drums and even tyres which look very good.

 Mike

I can recommend rustystumps myself Mike. Good company with some great kit.