Wolfram Research
Wolfram Math World: Unit Vector
This page defines the unit vector, a vector of length one in the same direction as a given vector. (The term "norm" can be interpreted in many cases as "length.") Provides formulas, references, and links.
Wolfram Research
Wolfram Math World: Radius Vector
Mathworld.com provides a very brief definition of the radius, or position vector. Also gives some properties of the derivative of this vector.