This one is low-cal and is always a crowd pleaser!
1/2 gallon raspberry sherbet, softened (Haagen-daz makes a low-cal raspberry sorbet which works just as well)
2 2-liter bottles of diet 7-Up or Sprite, chilled.
1 bag of frozen raspberries, thawed (keep and use the juice)
Puree the raspberries and strain to remove the seeds.
In a large punch bowl, stir the softened sherbet or sorbet, diet soda, and the berry puree.
Mix well