[URL="http://www.grandmanner.co.uk/"]Grand Manner[/URL] have a very large range of resin terrain, the largest I'm aware of in fact. It is predominately 28mm scale but they do have some in 40mm scale as well. They cover pretty much everything your average fantasy and historical player could hope for: Ancient, Classical Greek, Roman, Dark Ages, Medieval, East Asian, Napoleonic, American Frontier/Civil War, African, Middle Eastern etc.
There stuff isn't cheap, but they do have a good discount scheme:
Some favourites:
Dark Ages
Grain store
Watch tower
Medieval
Fences and Hedgerows