Flower flies are common and abundant during warm weather. Many appear to mimic bees or wasps, but vary tremendously in that mimicry. To get a really good idea of the astounding variety of syrphid mimicry, see syrphids on bugguide.net.
If you get a sharp photo, or use butterfly binoculars, you can recognize a syrphid fly by the spurious vein in its wing (5). If you see a syrphid holding just a little too still, look for a crab spider (6).
The Post Office has honored syrphids with a stamp in the Insects & Spiders set.