You could use Box: Buxus sempervirens, it's easy to trim into a form and is an evergreen. Thats what I use because it doesn't grow fast so it keep its shape very well. But maybe you need something for a warmer area? I lve in Holland and it can be really cold over here.

Sigrid

The Herb Rosmary(tuskin blue) is a easy plant to prune into a topiary type plant for a location that is mostly sunny.you need a light/well drained potting mix and a fairly large pot as this plant has a heavy root system.Most any plant can be pruned as a topiary plant.

I live in Anchorage, AK. (Zone ?) Have purchased 5 Chamaecyparis Thyoies "Heather Bun" and am wondering how best to store them over the winter. Temperatures generally reach 5 and 10 degrees but may go down to -20 for short spells. I have a garage that I could keep them in and a grow light that I could set for regular lighting. Could you help with some pointers?