Other
Alken Murray: The Phosphorous Cycle
A diagram which clearly illustrates the phosphorous cycle in a somewhat technical manner.
Geography 4 kids
Geography4 kids.com: Biogeochemical Cycles
Brief informational site provides the definition as well as explanation as to what Biogeochemical Cycles and what they do.
Other
Lenntech: The Phosphorus Cycle
A concise explanation of the phosphorus cycle. Also contains a flow diagram which illustrates the flow of phosphate through the cycle.
BiologyWise
Biology Wise: Carbon Cycle Diagram
Explains what the carbon cycle is and the basic steps in the cycle.
National Earth Science Teachers Association
Windows to the Universe: The Nitrogen Cycle
Interesting information on the Nitrogen Cycle as it relates to the Earth system.