On Mauna Kea (big island of Hawaii) the biggest sources of light pollution are the airports and harbors.

For the telescopes near big cities, I'm not sure if anybody has worked out the relative contributions of street lights to say billboards or car dealerships or backyard flood lighting. But from standing on the summit of Mt. Hamilton and looking down into the valley it would seem to be mostly street lights

I wouldn't be surprised. I mean, their entire purpose is to make it light outside. A neighborhood without street lights is noticeably much darker.

The only other likely sources are building lights and cars, and I'd think street lights far outnumber either of those in their ubiquity.

It depends on location, but in many places they actually are.