“What Eats?” is a great website that tells you what the predators and prey of any animal is. You type in the inquiry and up comes a list of animals that eat or are eaten by your input. Great site with lots of other tools, such as food web diagrams and videos. Some advertising.
Here's a pretty good detailed text of the comparison of a food chain and a food web for you to print and use or pull it up on your interactive whiteboard. Printable images to use as handouts too.
Games are a great way to help students learn. Here is a food web game for you to make for your class.
Have your class act out a food web. Here are the instructions.
Food Chains and Webs
Decomposers and Scavengers video here and teachers' guide for the program here from New Hampshire Public Television.