http://hotel04.ausys.se/pausch/comp/ppcomp.html: How to compute planetary positions
http://hotel04.ausys.se/pausch/comp/tutorial.html: Computing planetary positions: a tutorial with worked examples
http://www.braeunig.us/space/orbmech.htm: Orbital Mechanics (includes diagram)
http://www.physics.ncsu.edu/courses/astron/orbits.html: A Brief Explanation of Orbital Elements (includes diagrams)
http://www.go.ednet.ns.ca/~larry/orbits/kepler.html: Orbital Energies, Kepler's Laws and Other Relationships
http://www.amsat.org/amsat/keps/kepmodel.html: Keplerian Elements Tutorial
http://ssd.jpl.nasa.gov/elem_planets.html: Planetary Orbital Elements
http://ssd.jpl.nasa.gov/sat_elem.html: Planetary Satellite Mean Orbital Parameters
http://www.astro.queensu.ca/~wiegert/3753/3753.html: Near-Earth asteroid 3753 Cruithne