Personally, I like flowers and they are not that expensive if you buy them wholesale. Here are two sites:
http://www.growersbox.com/
http://www.rosesource.com/

I’m not sure where you are located, but the above wholesalers only ship to the U.S…..sorry. But if you are in the U.S., I highly recommend checking them out. I used rosesource for my son’s wedding and can vouch for their service.

Without flowers you can still do a variety of things, such as:

~ What about stacking favor boxes on a cake pedestal? Here is a link with a picture:
http://www.marthastewart.com/portal/site/mslo/menuitem.0e0eb51a2e6b5ad593598e10d373a0a0/?vgnextoid=216dc137bf22f010VgnVCM1000003d370a0aRCRD&autonomy_kw=favor%20centerpieces&rsc=ns2006_m6

~ Here is another link with a favor and centerpiece combination:
http://www.wanderfuls.com/

~ Sugared fruit always makes a gorgeous centerpiece and is simple to do.

~ Another thought: Have your parents, family and friends make copies of their wedding photos and place them in nice frames to use as centerpieces. Your guests can delight in the look of weddings past – especially with parents and grandparents’ wedding photos.

~ You can still do candles even though it’s daytime. I reckon candles are nice anytime. Perhaps something with a floating candle? This site has lots of thoughts:
http://www.surroundings.com/

Excellent luck!