http://itsamadworld.com/

This is more of an open-ended, where students have to generate their own word lists. Very fun.

http://www.funbrain.com/brain/ReadingBrain/Games/Game.html?GameName=MadLibsOnceUponA

This is a safe website that is fun, and allows students to pick nouns, verbs, and adjectives from a long list, so the students won't be embarrassed by getting the answer wrong.

http://flubaroo.com is a great site if you're using google forms or spreadsheets.

I was recently introduced to www.bubble.us and loved its simplicity, and its professional look.