Small Bee
I’m not sure what sort of bee this is. They seem to be fairly common. It’s hard to tell scale from this picture but the bee is not more than 10mm long and possibly a little less than that. It moved from flower to flower fairly quickly so it was a fair job keeping up with it but I managed to get a few that are probably good enough for someone who knows these things to identify it. If I get a name, I’ll update the post.
Update: The good folks at BugGuide.net have identified this as being in the genus Ceratina, the small carpenter bees.