(Onions and sprouting watercress tops)
Here’s a great idea from Design Sponge: combine vegetables with leafy greens to make an remarkable centerpiece.
(Squash and some kind of flowering green)
The idea is to pick a colorful veggie–squash, eggplant, etc.–and then pick a bunch of greens–herbs, green onions, a flowering lettuce–and put them together. First, cut the greens and tie them. Then insert a skewer or a stick into the veggie. Finally, combine, like so:
(Carrots and beans)
There’s a more thorough how-to on the site.
I like this idea because it is the kind of centerpiece that is unusual and visually fresh while still beautiful. Plus, instead of throwing the centerpiece out afterwards, you can eat it.