Storyboard That has an extensive database of images for you to use in your storyboards.
Type in something you want into the “Search” field. If you want more results hit the “More...” link on the left. Use category names like “food” or “Shakespeare” if you do not get the images you need at first.
Photos for Class / Photos for Work
Premium users have access to Photos For Class through the search feature as well. You can adjust what kind of images appear in your account settings.