Wood Blocks have been one of Children's favorite educational toys. Be careful when selecting wood blocks, you need to select either maple or beech wood block.
Educo Maple Block Set- 50 Pieces

Has a lot of different sizes of wood blocks for the kids to build different types of structures

Metro
From: 2Blockheads.com
Cheaper blocks do not last as long and may not be as safe for your children to play with.

Educo Maple Block Set- 50 Pieces