I haven't seen one of these in a few months. I assume they're moving back south after breeding in Arctic regions. It's a Say's Phoebe (Sayornis saya), a little flycatcher that is doing pretty well, because it adapts well to human developments (nesting in and around houses and other buildings).
They may be common, but I've only seen them around the little pond on our west campus, usually in the same places I often see the Black Phoebes. I'd like to get a few more pictures on a sunny day, as these are just a bit fuzzy in the gloomy gray conditions we had today (but I don't mind the rain! We really need it out west).