One of the things I miss from the couple weeks I took metro to work every day was the musicians. Almost every time I see a street musician doing something even reasonably close to what I would consider music (sorry, beating trash cans doesn’t usually count for me) I try to give them something for making the area a little better.
Here’s an interesting WashingtonPost article along similar lines, except with a twist. Also of notice, they’re beginning to learn the concept of embedding different media formats.