R.K.
How about a 'people scavenger hunt'? You make a list of questions about the people who are attending such as:
Who's favorite color is_____?
Who never misses an episode of ____?
Who loves to garden?
This way everyone has to mingle and talk to each other. I would do between 10 - 20 questions depending on how many people are going to be there. You could offer a prize such as a gas card for the most correct answers in 30 minutes.