Give guests bandaids to stick on interesting places on their bodies. Children with a theatrical bent enjoy this one. Write the name of, or place a picture of, each plague on separate cards. Have guests choose a card out of a bag, and act out their Plague. Give them 5-10 minutes to prepare a skit.
Adults can judge the results and hand out a prize to the group presenting the best re-enactment.
We've been doing what he tells us Mixing straw with clay. Laugh - Tell the story, but with mistakes for the participants to catch. One family uses a large hard-cover Haggada, with several blank pages before the text. Each year, they write down the names of guests. Videotape the seder, get grandparents and other senior members of the family to say a few words or share one of their own Pessah memories from their childhoods.