For basic addon coding for wow I used wowwiki's pages and looked at the coding for addons doing similar things.
For my first infopanel plugin I used Scott's combatlog and minimap plugins to see what was needed for it to work. I also used things like nUI_Healbot to see how you connect existing addons to nUIs info panel system.
For the LDB addon I wrote I used DBMs own LDB addon as it is very clear in there as to what each section does.
And finally .. to help those that want to learn I try to add as much commenting in my addons as possible.
It takes time and lots of trial and error in some cases but once you get there its hard to leave ..
