Flower pots - because they were relatively cheap, and the material is somewhat "natural" (well, as natural as clay can be after it has been shaped and kilned - it is still reminiscent of stone). When coupled with coconut fiber, they look like little thatch-roof cottages. Which can be a disadvantage: Burninators are naturally attracted to thatch-roof cottages.

Plastic leaves - cheap and aesthetically pleasing. Plus, they don't die like real leaves do. And they provide "cover" for the snakes to hide under/behind and climb on. I have three types: Ivy leaves, ferns, and cattails.

Branches - give the snakes something to climb on. The ones in there now are a hardwood from a tree I cut down for someone a while back.

Bamboo - again, cheap. I found some in a trash pile someone was tossing out. Make great "tunnels" for the snakes to hide in. Plus, if I want to transplant a particularly skittish snake, all I have to do is coax her into the bamboo, then pick it up and move it where she needs to go.

Hard plastic tree - it was on sale at Wal-Mart, and it gives the snakes something to climb up on.

Bricks - when broken up, look like natural rocks. Cheap, too. Gives the snakes something to rub against when shedding.

Paving block - in the water enclosure, gives the snakes something to rest on when they get done taking a swim. I've drilled holes and mounted ivy leaves for them to climb on, if they so desire. I also put a flower pot in there for them to hide in, if they so desire (and they often do).

All in all, with my enclosures, I try to simulate a natural environment as much as possible.