Astro-logix
Create complex and beautiful fractal stars and 3D geometric shapes.
http://www.astro-logix.com/

Atollo
Flexible models, from articulated figures to geometric space structures.
http://www.atollo.com/

Gridblox
Cubical wooden blocks with notched corners that interlock by gravity.
http://www.aptitude-testing.com/gridblox.htm

Kapla USA
Wooden construction blocks from France, with a long thin shape, and books with suggested projects. Provides photo gallery of museum exhibits, and workshop information.
http://www.kaplaworld.com/

Link-Kit
Also known as Omagles, a building toy to create an unlimited variety of child-size toys for climbing, riding or pretending.
http://www.omagles.com/

The Construction Site
A large variety of construction toys including brand names such as t.c. timber, K'nex, Lincoln Logs, Tinkertoy and Exin Castles.
http://www.constructiontoys.com/

Wedgits
Wedge shaped building blocks construction set. Includes design ideas and worldwide list of dealers.
http://wedgits.com/