Building Blocks -
http://www.gse.buffalo.edu/org/buildingblocks/
This is the outline of a program of using blocks, puzzles and
other manipulatives to reinforce mathematical concepts. A good
read; excerpts excellent for handouts.
Wooden Blocks by Barclay -
http://www.barclaywoods.com/
This is the ultimate block site; examples of creations made by
blocks; value of blocks; instructions on how to make your own
wooden blocks.