Hot Seat

One student sits on a chair with his/her back to the board, facing the rest of the class.  The teacher writes a word/phrase on the board behind the student, and the rest of the class must describe the word (without saying it) to the student in the 'hot seat'.

This can be done in 2 teams, each describing the word to their own representative.  You can have a student from each team sitting on the hot seats at the same time if you don't mind increasing the noise level a little bit.