There's lots of public art at CTA stations. There's a whole list of all the art by station on the CTA site. According to the site, "Many of the pieces are a result of the Arts in Transit Program, which is funded by the Federal Transit Administration and coordinated locally through the City of Chicago’s Department of Tourism and Culture. A number of other pieces were created through the CTA’s Adopt-A-Station program and through partnerships with organizations such as the Chicago Public Art Group."

See also:

public art in Chicago