You can check out:
Internship Oppurtunities at 20th Century Fox
Link to everything Disney
Good site for the most recent internship and job listing in entertainment
Link to the HBO internship program
Everything you need to know about a Jim Henson internship including FAQ's
Northwestern University's television internship selection
Northwestern University's film internship selection
Stanford's TV and Film Internship site
Internship page and application for Lucasfilm
Year-round MTV Internships
Get That Gig
Mosaic Media Group, This is a chance to work with Eric Gold
Another good MTV site
Search more on Wetfeet.com

Major studios:
Paramount
Sony Pictures
Miramax
MGM
Dreamworks
Universal