Physics Classroom
The Physics Classroom: Motion and Forces in Two Dimensions: Vector Addition
An extensive discussion of vector addition with links to interactives and exercises.
CK-12 Foundation
Ck 12: Vector Addition
[Free Registration/Login may be required to access all resource tools.] A collection of resources on how to add vectors.
NASA
Nasa: Vectors
This site from NASA provides an excellent tutorial on vectors and their use in physics to describe the motion of objects. Vector addition and resolution are illustrated.