The Association of 16mm Modellers
This one is all you really need, as not only does it have loads of stuff about all things 16mil, its own links page has many more than we could put here.
To save you hunting for it, the page in question is here.
But if you really want more, your webmaster's own site includes photos of many of our garden railways and indoor layouts.
The site also has a number of articles on related topics.
And if videos are your thing, Rob Guinness has considerably more then 200 on his Youtube channel.