Here is my other vote for most beautiful bee: the cuckoo bee. They are a lovely shiny, metallic blue or green, with a detailed surface all over their body. They usually don’t sting, and are a type of parasitic wasp.
Their larvae are ectoparasites (external parasites) of other bee and wasp larvae. The name “cuckoo wasp” comes from the fact that this insect, like the cuckoo bird, lays her eggs in the nest of an unsuspecting host.
Many more lovely photos here.
Photo via Wikipedia.
EDITED 12/19/08 TO ADD: Some folks have taken me to task for using the word “bee” to describe this wasp. Please note I did say it was a parasitic wasp, and give it’s correct family.
Common names are tricky. These insects are called “bees” in the same way that many people call anything with 6 legs “bugs.” I don’t bother with being strict about common names, because while the ESA may regulate them, most Americans have no idea what the “proper” common name is. And could care less, frankly.
I’m not writing this blog just for entomologists–it’s for the general reader that just happens to like bugs. Chill out, folks.