If you want non.flower centerpieces you can have so many other options to use.....like you can use paper decorations with some balloons.....
http://socialcouture.typepad.com/.a/6a00e00998c5c888330134869bafba970c-350wi
http://images.marthastewart.com/images/content/pub/weddings/2008Q2//mwd103418_spr08_025_xl.jpg
you can use shells, pebbles, stones with photo-frames etc...
http://t0.gstatic.com/images?q=tbn:ANd9GcTicmycXmYW0mwsXo0UIcx0BcEY_QBNu6QNOIHlsnAxvPoI8QF5cA
What about some fruits Centerpieces....
http://chezwedd.com/img/centerpiece4.jpg
I personally like candles and Lanterns.....