Hi Brandon,
Here are a few references that are interesting (i.e fascinating):
- Jazen, D. H. (1967) Interaction of the bull's-horn acacia (Acacia
cornigera L.) with an ant inhabitant (Pseudomyrmex ferruginea F.
Smith) in Eastern Mexico.  University of Kansas Science Bulletin,
47:315-558
- Ants of the genus Atta and the mushroom they farm (sorry, I can't be
more specific)
- Beetles of the family Scolitidae and the fungus associated with the
different species
- The male ichneumonid wasp Lissapimpla excelsa and the orchid
Cryptostylis subulata. (orchids are a good source of examples of
insect-plant mutualism)
- Bees and the flowering plants are another example of
co-evolutionnary mutualism.
Hope it's usefull
Philippe