Here in the Salt River ward we are really enjoying our singing time. This last week I used the birthday candles idea that I found on sugardoodle.net with the junior primary. If you are not familiar with it, it goes like this. Have children stand with their hands clasped over their heads to pretend to be candles on a cake (everyone else), when the birthday song is over the child gets to blow out their candles.
For senior primary we played a version of "Don't forget the Lyrics." I pulled the microphone off the podium and had one child come up, select a song, then choose two additional kids to come up. All the children in the audience would sing until I held up the stop sign then the person holding the mic had to finish singing the line. They weren't very good at it, but they had fun trying.