The ideas below are designed for centerpiece-makers who don't boast great crafting skills. Hotshots with hot glue guns can, of course, tackle much more complex projects.
Buy flowering potted plants. Wrap each ugly plastic pot in either pretty wrapping paper or heavily spray- starched calico. Tie with a broad ribbon. This can look elegant rather than "country" if you choose white flowers, a white wrapping paper with a white-on-white pattern, and silver or gold wide wired ribbon. Or use your wedding colors.
For this centerpiece, you buy a nicer and larger glass bowl than is usually used for floating candles- something closer to the size of a small mixing bowl or fish bowl. Look for something with a pattern that accentuates your wedding theme-discount department stores often have interesting dishes for a few dollars each. Then use the larger floating candles-perhaps the ones shaped like flowers-or more than one candle per bowl. Make sure the people who get the centerpieces know where to empty the water from their bowls!
This requires more skill and patience. Craft stores stock Styrofoam rings that will fit around pillar candles. Cover the ring with silk flowers and ribbon, put a color-coordinated pillar candle in the center, and you have a centerpiece! The part that calls for patience is putting the flowers in the Styrofoam. You can simplify that part by wrapping most of the ring in wide ribbon, then attaching a "pouf" of flowers on one side.
Look at craft stores for topiary forms that are already set in pots. If you start with an assembled form, all you have to do is cover the "ball" part of the tree, usually with some sort of filler material and then a scattering of silk flowers.
Choose wood or metal containers at your local craft store. The choices include buckets, mailboxes, and other shapes. You can paint the container in a solid color or leave it plain. Use rubber stamps to create designs in paint. (Small containers of craft paint will usually have an aisle to themselves in the craft store-make sure the kind you choose will stick to the material you're painting.) Fill the finished container with silk or live flowers.
Alternatively, try decoupage! Look in your craft store for how-to books. Wrapping paper is a convenient source of decoupage designs, but you can also find books of decoupage cuttings.
Craft stores often have really big seashells. Fill the opening with florists' moss and stick silk flowers (preferably imitating rock garden flowers) in the moss.
If your wedding has a theme, is there something theme-related that can either be filled with flowers or decorated? This idea works well for themes like teddy bears (stuffed bears are everywhere and easy to dress) or Mexican Fiesta (pinatas!)… perhaps not so well for themes like fish or Famous Poets.