(Above) These skewers from Slashfood are arranged like flowers and made from tortellini, tomatoes, and mozzarella balls.
(Above) This edible centerpiece featured on Elizabeth Anne Designs is made with a styrofoam base and strawberries. Note the dipping sauces on the table. Yum!
Or how about this simple, chocolate-covered strawberries centerpiece from this flickr photostream?
(Above) This professional fruit arrangement is expensive but could be easily replicated.
The amazing couple over at This Young House used lemons and limes for their centerpieces (above).
Another idea is to use candy for edible centerpieces. I've seen lots of candy buffets (like the one pictured in this flickr photostream) but I haven't seen it used as centerpieces. I think it would be best to use wrapped candy, so leftovers wouldn't go to waste.
Just for the record, I think centerpieces are among the last things we should worry about as we plan meaningful and memorable weddings that focus on community, commitment, connection, and fun. In fact, I've been to weddings (and restaurants) where the centerpieces are so big and distracting that they actually hinder community, connection, and fun because you can't see the people across the table!
But if they are on your list of action steps, hopefully these ideas are useful.