http://extreme-macro.co.uk/ A UK Based extreme Macro teaching Site.
http://www.naturesphotos.co.uk/ Natures Photo’s. Sign up on the Mailing List for the Newsletter, an example of which is http://www.naturesphotos.co.uk/media/PDF%20Files/Downloadable%20mailings/(25)_Occasional_newsletter_59.pdf
http://zerenesystems.com Home of Zerene Systems who produce Zerene Stacker
http://photomacrography.net Home of a US based Photo Micrography site
http://www.heliconsoft.com Home of Helicon Soft who produce Helicon Stacker, an alternative to Zerene Stacker