Looking at Some specimens collected a few weeks ago when it was last warm (March 24th!) I am wrestling with Ceratina sp. using the keys at Discoverlife.org Here is the Bee genera key. When you get to a genus, then click on its name and you will get the keys available to take the ID to species.
Unfortunately unlike birds, in order to identify almost all kinds of bees to species, you have to get them under a microscope. and have them hold still So you have to kill some of them to learn about them. For good specimens of fuzzy insects like bees you have to have them neat so you can see the relevant characters for identification, I have been blow drying my bumble bee specimens for a few years now as explained in this presentation by Sam Droege at the USGS Bee Lab, although I use my hairdryer for now. I think I may will start gluing bees to pins instead of piercing them per this Viideo.
I need lots of practice, but expect to have fun! Thanks Mark.