Here are some descriptions of the common groups of bees.
There is a formal academic study about sunflower bees in the southwest. You can find it here
The best way to learn your bees is to take the Bee Course.
The bible of bee literature is Charles Michener's Bees of the World. The second edition was just published in 2007. Mich should be an inspiration to all of us. T
Charles Michener teaching about bees.