Rectangular trays create drama
Copper trays contain Irish moss and Scotch moss. They don't have drain holes but work well for temporary display (2 - 3 weeks).
Irrigate about once a week and drain excess water by turning each tray upside down over a sink (with one hand over the moss to keep it in place). Or drill drain holes in the bottom and display trays on pavers or plastic.
For a similar effect, substitute wood boxes.
Copper trays: 6 1/4 inches square by 1 1/2 inches tall; $9 each from Smith & Hawken (800/981-9888).