During presentations, each student completes a "You be the judge" sheet. This involves quickly marking each group against specific standards. Afterwards, groups discuss their ratings and complete a group nomination form, nominating their favourite group and explaining the reasons for their choice. Students hand them into a 'nomination envelope'. From this I can pull out the envelopes, a la the Oscars, and read out the results.
By hamming up the process into a ceremony students stay engaged as well as learning how to give feedback to one another. The nomination cards are also great certificates of achievement that the winning group can take away with them.
I can't get box.net to work on the network so I will wait until next time I'm on my home computer to upload these items