Opportunities abound to conduct research off-campus during the summer. Most summer positions are paid and last approximately 10 weeks. These programs are good way to experience and get to know other universities and their faculty, which can be especially useful if you plan to apply to graduate school in the future.
The application deadline for most summer research internships is in January and early February, so you should start to put your application together early (e.g., December to early January) and give your letter writers plenty of advance notice.
NSF's website for Research Experiences for Undergraduates
REUs are the National Science Foundation's summer research programs for undergraduates. As an REU student you are granted a stipend to work with professors or other researchers at a host institution for 10-12 weeks during the summer. Each institution hosts 10 or so REU students. REU application deadlines are in late January or February (the exception is the Cerro Tololo Inter-American Observatory's REU, which takes place during the Chilean summer January-March and so has an early October application deadline).
A comprehensive list of astronomy REUs can be found at:
NASA offers paid summer research positions in its locations ranging from Goddard Space Flight Center in Maryland to the Ames Research Center in California. The range of research opportunities is broad, including robotics, space instrumentation, astrobiology, and solar physics. The application deadline is in January.
Department of Energy's Science Undergraduate Laboratory Internships
The U.S. Department of Energy sponsors paid research internships at national labs across the country. The applications deadlines are in August for fall internships; November for spring internships; and April for summer internships.
Space Sciences Laboratory Summer Fellowships
Choose an SSL researcher whose work you're interested in and ask him/her to be your sponsor. The application deadline is in May.
UC Berkeley Summer Research Opportunity Program
The University of California, Berkeley sponsors a Summer Research Opportunity Program (SROP), offering students opportunities for faculty-mentored research in the fields of Astronomy, Astrophysics, Chemistry, Computer Science, Earth & Planetary Science, Geology, Geophysics, Mathematics, Physics, and Statistics. The eight-week program is held on the UC Berkeley campus. The application deadline is in February.
Space Telescope Science Institute summer program
This program takes both US and international students. STScI manages the science mission of Hubble and of the next generation James Webb Space Telescope for NASA and provides a very dynamic science setting. The application deadline is in February.
NASA - Houston - Planetary Sciences
NASA - the Lunar and Planetary Institute invites undergraduates with at least 50 semester hours of credit to experience research in the planetary sciences. As a summer intern, you will work one-on-one with a scientist either at the LPI or NASA Johnson Space Center. 10 week program. $5,000 stipend and $1,000 travel expenses for US or $1,500 for foreign nationals. The application deadline is in January.
SAMSI Undergraduate Modeling Workshop
Summer programs offered to learn statistics and data-modeling techniques. Application deadlines vary.
Research in Industrial Projects for Students
Exceptional undergraduate students of mathematics, engineering, computer science, and physical and life science disciplines are sought, to apply to this unique summer research program. Past RIPS project sponsors included Arete, Symantec, Amgen, Pixar, JPL, Lawrence-Livermore and Los Alamos National Labs, and others. 36 students will be in-residence at UCLA for nine weeks.
[Attended and recommended by former UT Astronomy student Agnes Kim] Teaching Assistants act as tutors and mentors, and assist students in using astronomical equipment and personal computers, under the direction of two senior faculty. They also organize recreational and social activities, and deliver one or more lectures on topics of their own choosing. Applicants should be graduate students, graduating seniors, or rising college seniors, majoring in physical science or engineering. SSP alumni are especially encouraged to apply.
Northwestern University's Materials Research Science and Engineering Center (MRSEC)
The Materials Research Science and Engineering Center (MRSEC) at Northwestern University offers a 9-week, paid summer research experience for undergraduates. The students are paired up with some of the leading research professors in science and engineering fields. Research areas include ceramics, polymers, nanocomposites, photonics, nanoparticles, molecular electronics and biomaterials. While there are many REU programs, the NU-MRSEC stands out in offering students an interdisciplinary research experience.Students currently pursuing an undergraduate degree in science or engineering who are US citizens or permanent residents are eligible. Participants are paid a $4500 stipend, a travel allowance, and on-campus housing is provided.
ASTRON/JIVE International Summer Students Programme
In the Netherlands. The Programme enables astronomy students (graduate or advanced undergraduate) to spend the summer (10 to 12 weeks) at the Dwingeloo Observatory, conducting astronomical research under the supervision of ASTRON and JIVE staff members. The application deadline is in February.
International Astronomical Youth Camps
A three week program in Europe for students ages 16-24 from around the world, and whose common interest is astronomy. The application deadline is in April.
Many universities, laboratories, and observatories have their own undergraduate research programs. If there's an institution you'd like to work at, odds are they have some sort of program for you! Some useful links which have partial lists of these other opportunities are given below.
The American Astronomical Society's summer employment opportunities