Write the words for one sentence on the board in mixed-up order. I usually use a single column format, with all the nouns together, pronouns together, etc.
Students work individually to arrange the words into a grammatically correct sentence.
When they think they've got it, they cal you over to check. You can set a time limit to provide a little more structure. When the time is up, they can compare their answers with a partner or you can ask one or two students to write their sentences on the board. It's a fast paced fun game that really gets students thinking about grammatical form and syntax. It requires some preparation on your part, but if you keep the envelopes you can recycle them over and over again.