Major universities in the US, as well as medical schools, Federal agencies and corporations offer hundreds of summer research opportunities for students in all fields. Spend 6-10 weeks this summer and earn between $2000 and $5000 for the chance to do research with world-class faculty. Besides earning more than you would make at most summer jobs, you can also create a research network with professionals in your field including faculty who can write reference letters for your applications for graduate or professional school. Most of these programs are in the sciences, many are designed to attract students from groups under-represented in the relevant disciplines, and most are designed to help the institutions increase diversity of PhD programs (some are for pre-meds).
The sites below are excellent sources of information about available summer research opportunities and where to apply. None is inclusive of all summer research opportunities, so check multiple websites. Generally, they require an application with a statement of purpose (a description of your development as a scholar in your field thus far and why summer research would help your professional development), a resume, and letters of recommendation. Deadlines vary but generally start in January and continue through the spring. The most competitive programs tend to be earlier. You can also Google "undergraduate summer research" and refine it by school or by discipline. Go for it!