A good way to explain the Isosceles Triangle Theorem: The two sides opposite the two congruent angles are congruent. Draw an egyptian pyramid on the board and explain that when they started building the pyramids, the only way they knew that the two sides going up would be congruent, was to precisely measure the two base angles and ensure they were equal.

Note: the base angles of the Pyramid of Giza (below) are approximately 51.5 degrees