Ours is kinda like Emantha's. We use Hawaiian punch, one can or 64 oz bottle (not concentrate) and a 2 liter of Sprite. That alone is good, but you can also add some vanilla icecream or a sorbet/sherbet to make a frothy fizz which is really cool too.
Some ladies at church made a rhubarb punch for our wedding that went over very well. All they did was take a bunch of rhubarb (to taste) cook it down with a little bit of sugar as you would for pie (like apple sauce). Cool then add to Sprite or seven up and add the vanilla ice cream, about 7 scoops. The icecream not only tastes good, but also keeps the punch cold without watering it down, like ice cubes would.
Just wanted to add, a rainbow sorbet/sherbet would be awesome in the Hawaiian punch one.
Also, you could just buy a few fruit necters, can find int he single can, and mix with the Sprite or 7up. Would be very yummy.
Oh, one more, how about a Cranberry juice, my favorite is Crancherry, and some sprite. It you are worried about too much sugar, go ahead and use diet soda. We do and it doesn't change the flavor enough to notice. Of course you could make a smaller batch of the diet and the regular catering to both sides.
i need a punch recipe! 
