This is one of the best all around sites that I have
found. It is titled "The MacTutor History of Mathematics
Archive."
http://www-history.mcs.st-and.ac.uk/~history/
This is an award-winning site that links
to all sorts of mathematics information.
http://archives.math.utk.edu/
This site has practice with classifying triangles.
http://www.onlinemathlearning.com/types-of-triangles.html
This site investigates the exterior
angles of a triangle:
http://www.regentsprep.org/Regents/math/geometry/GP5/LExtAng.htm
This site investigates properties of
isosceles triangles:
http://www.geom.umn.edu/~dwiggins/conj13.html
