Photo from the 31st Academy Awards, photo from Wikimedia Commons
When searching for movie reviews online, bear in mind that many professors prefer that students use reviews by journalists and other professionals. Always evaluate your search results: Is the review signed? Is the website a news outlet or other trusted site? Is the style one you would associate with professional writing? When in doubt, ask your professor. Here's a few hand-picked resources to get you started:
Several of the library's databases have movie reviews. Here's a step-by-step lesson in how to find them.