Georgia State University
Georgia State University: Hyper Physics: Proton Proton Fusion
A look at the reaction that fuels the Sun with this diagram of the nuclear fusion process.
US Department of Energy
Fus Ed Web: Physics of a Fundamental Energy Source
An excellent resource on nuclear fusion! Using incredible graphics and excellent discussion, this site (with its several pages) provides an exhaustive online course on the topic. Click on the link for "a Guided Tour" and begin.