Good vase fillers for flowers should be water-resistant and large enough to stabilize the flowers but small enough so the filler lets you insert the flower stems. Marbles are a good choice because their round shape makes it easy to poke flower stems through to the bottom. Clear or colored glass can offer a creative touch. For really tall stems, place a handful of pennies or other heavy, flat fillers on the bottom to help keep the vase from tipping over.
Clear vases are dressed up with almost any type of vase filler. River rocks, seashells and colored glass pebbles add a decorative touch. Beach glass makes an attractive vase filler and can be used in dry vases or vases filled with water.
Dried staples like coffee beans and pasta are attractive vase fillers. Beans from a dry goods store come in a wide variety of shapes, colors and sizes. Hard candies like lollipops are fun to use. Larger nuts like walnuts, Brazil nuts and others make for an interesting change of pace.
A wide variety of plastic objects make interesting and colorful vase fillers. Look for cheap items that are not too flat so they will fill out the vase nicely without stacking. Different color Lego blocks and small dimestore toys make interesting displays. You can even use small dolls or stuffed animals as vase fillers. At Christmas time, use small tree ornaments--at Easter use plastic Easter eggs.
Plants like paperwhites and small bamboo can be grown indoors in vases. Good vase fillers will allow the roots to penetrate, so round glass beads or marbles are a good choice. Clear glass allows you to see the roots as they grow and has a striking effect.