Neal's Yard, WC2H 9DP
This is one of the most established collections of wholefood and related businesses. They are not cheap, but you can find obscure and unusual stuff here.
They apparently used to have a website at http://nealsyard.net/, but this seems now to redirect to someone's personal site.
However, most of the business units seem to have their own websites, which come up on a search -- try http://www.google.com/search?q=neal%27s+yard -- for example:
- Neal's Yard Salad Bar -- decent vegetarian and vegan food; though it's not totally unique in London these days, it's central and convenient, and it's been around for a couple of decades now.
- Neal's Yard Remedies -- All sorts of natural remedies sold by Neal's Yard.