Propagation of Woody Plants by Cuttings -- Brent Walston
The owner of Evergreen Gardenworks, an excellent source for traditional, rare and unusual species of plants for use as bonsai, discusses the best techniques for propagation from cuttings.

Ramification of Bonsai -- Craig Coussins
International Bonsai author and lecturer, Craig Coussins, gives some tips for building ramification and twig structure.

The Maple Year -- Craig Coussins
Craig Coussins gives a season-by-season to-do list for Maples.

The following articles are hosted on other sites and are excellent resources for different areas of bonsai interest:
 
Recipe for a Bonsai Bench -- Ken Wassum
Bonsai look much better on a good bonsai bench. Ken Wassum shows you how.
 
Collecting Trees from the Wild -- Walter Pall
A very thorough article on how to identify, prepare, dig, and care for bonsai trees collected from the wild.
 
Collecting Basics -- Will Heath
A good article that covers collecting from the wild, nurseries, and urban areas.
 

Great sources for additional articles
Evergreen Gardenworks
Bonsai Information by Craig Coussins