Opt for a terrarium centerpiece. They can be a fun DIY project, they make great home decor (i.e. recycling) and they aren't your run of the mill centerpiece which will remind people of your unique taste.
Or choose a potted plant that can be reused in your home or act as favors.
Another option? Go non-floral altogether like this board by bride2be via StyleMePretty. Try shells, cotton, or cakes.
As for bouquets...