Steve's Photo Site

Manufacturers and Importers

Canon Nikon Fuji Kenro
Olympus Sony Leica Cameras Tamron (USA)
Panasonic Samsung Sigma Tamron (UK Importer)

Hardware

SRB-Griturn Makers of bespoke adapters such as reversing rings and coupling rings.
Lens Buying Guide This is really an advertisement, but it does contain a useful guide to different types of lens.

Retailers

Jessops  
Wex Photographic Used to be Warehouse Express.