I did a lesson on the tangram for a math class I just completed. In the process I found some wonderful resources on using tangrams in math. I thought they might be of interest.
This link tells a class story using tangrams
This has several tangram puzzles to watch and solve It is my favorite.
A site to solve tangram puzzles.
Solve tangram puzzles.
Tangram puzzles to solve.
Various shapes to fill.
Tangrams patterns to cut out.
An entire site devoted to tangram puzzles and using them in the teaching.
Lessons, books, web sites, and shapes.