Other
Synthesis Definitions
Includes all different types of synthesis, including FM, additive, AM, subtractive, granular, RM, and wavetable.
Stanford University
Percussion Fm Synthesis
Interesting site on the technical side of FM synthesis, including how to make different sounds. For either the very curious or very advanced student.
Other
Tutorial for Frequency Modulation Synthesis
Exactly what it says - a tutorial for FM synthesis. Includes information on calculating sidebands, C:M ratios, and calculating the fundamental frequency.