MathBits: Geometry Menu

Polygons

Shmoop: Polygons

Shmoop: Angles in Polygons

MathIsFun: 2D Shapes

MathIsFun: Polygons

MathOpenReference: Polygons

MathBits: Polygons

Triangles

Shmoop: Triangles

MathisFun: Triangles

MathIsFun: Interactive Triangles

MathBits: Triangles

MathBits: Right Triangles

Quadrilaterals

Shmoop: Quadrilaterals

MathIsFun: Quadrilaterals

MathTrain: Quadrilaterals

MathIsFun: Interactive Quadrilaterals

LearnAlberta: Exploring Shape Classification (flash)

Illuminations: Angle Sums

MathIsFun: Interior Angles of Polygons

MathIsFun: Exterior Angles of Polygons

MathBits: Angles of Polygons

Circles

Shmoop: Circles

CoolMath: Circles

Math.com: Circles