Stone. Substitute stone for the pavers. There are several beautiful varieties available in many different shapes and thicknesses. You can work with the pieces exactly as they come from nature or have the stones cut to your specifications. You also can experiment with different edging materials.
Concrete. Fill the entire bed with concrete. Use stamps or stains to add texture or color. Divide the bed into quadrants, and use one material in the upper left and lower right sections, and a different material in the other two quadrants.