The National Science Foundation sponsors the Research Experience for Undergraduates (REU) program in which undergraduates (typically, but not always, between their Junior and Senior years) are paid a stipend to work on a research project at universities and laboratories all over the United States. Typically, but not always, students travel to an institution other than their own. REUs pay well and are great opportunities to expand one’s horizons. Applications are highly competitive.
You can access the University of Colorado application on the Physics REU site.