This site is from the Children's University of Manchester and is a fun way for your students to learn about adjectives.  It includes a learning module, game, and quiz and teaches your students about adjectives, superlative, and comparative.  This is a great site to use full screen  on your interactive whiteboard to teach the whole class or have the students work on the site individually!  There are also other activities that could be used as well.  Check out Adjective Detective!