Here is a list of the places I feel are the best to find an internship in the tech industry. Tere is a varity of resources here that allow you to search for internships and post your resume to find an intern position. The resources here also include links to other useful internship topics, including international internships, resume writing for interns and lots more.
As the name implies, tech interns offers information about intern positions in the technical field. They specifically post internship openings in science and engineering.
Experience.com is one of the largest new grad and internship databases available. They have a comprehensive intern jobs database as well as tips for resume writing and networking.
Engineering Central provides information about regular and intern job postings for all engineering disciplines. This is a great place to check out mechanical and electrical engineering internships!
CollegeGrad.com provides job listings for new grad positions as well as internship opportunities in a variety of industries, throughout the U.S.
InternWeb provides access to intern opportunities in many industries. They were many technical internships available here when I checked. The positings are free to employers and job seekers, which makes it a site that is affordable for even the smaller employers.
InternshipPrograms.com is another site that provides comprehensive internship opportunities in a wide variety of industries. There were many tech positions listed here when I checked.
CDS provides job links and comprehensive resources for international internship opportunities. CDS also provides study abroad resources and visa assistance to students.