Purple Math
Purplemath: Graphing Exponential Functions: Intro
An in-depth lesson which teaches you how to graph exponential equations. Examples are worked through step by step and explained in detail for different exponential equations.
Khan Academy
Khan Academy: Mcat: Physical Processes: Atomic Nucleus: Decay Graphs and Half Lives Article
Explains how scientists can tell when radiation has been leaked, how to read a decay graph, what we mean by a half-life, and what carbon dating is.