In the Washington, DC area:
Most DC Metrobuses look more or less like this. There are a lot of minor variations, but the white background with two red stripes is the basic livery. It is inspired by DC's flag.
Here's another version that illustrates how some of the different trunk routes have slightly different
paint schemes. Compare the top of this bus with the top of the first one.
Metrobus also has a lot of buses wrapped in this "go green" livery, to advertise transit's environmental friendliness.
The most recent order of buses has a new livery, which looks like this:
(Photo by Richard Layman
MetroExtra, Metrobuses version of limited stop service (similar to the Metro Rapid in LA) looks like this:
(Photo by Rob Goodspeed.)
The DC Circulator runs on some key routes in central Washington. When DC's streetcars start running, they will have a similar paint scheme.
Arlington County's ART service:
Fairfax County Connector, sometimes called the ketchup and mustard bus:
Montgomery County Ride-On. There's also a green version:
There are bunch of smaller agencies, but those are the main ones.