For painting, Tokyo or New York skylines (or Vegas), because there a lot of nighttime photos of them online.
Lots of hues, fun to paint.
For line-art, city streets. Harder to find photos of them online though. Ooh, or a strip mall, because of the various angles and lines. Also, if you can snap a photo yourself of a strip mall, there should be people, which helps in the practice. Sometimes, online photos of strip malls are taken at odd times to avoid people standing on the sidewalks.
Practicing on background people helps me a lot, because I have to remind myself to think of them more as shapes/silhouettes than detailed objects, like a main character. Not that detailing background people isn't a style of it's own.