For general information on sundials:

Sundials on the internet
www.sundials.co.uk

British Sundial Society
www.sundialsoc.org.uk

North American Sundial Society
www.sundials.org

For fine historical replicas of brass sundials and scientific instruments,
I recommend Dr. John Davis of Flowton dials.
www.flowton-dials.co.uk

Not a sundial site, but a gallery of close up or 'macro' art photography of flowers, botanicals and garden art by Roger Smith.
www.jurassiccoastgallery.co.uk

Mike Shaw's fun website of favourite sundials
www.wiz.to/sundials

Sundials in Ireland
homepage.ntlworld.com/michael.j.harley