I just have some of the fake wood and roots that I found from Petsmart. I tried to keep it more natural looking but also think some of the other ones they sell look pretty cool.

I have some of that fake coral in a my tank that Petsmart sells, also have a bubbler that is a chest that opens and close as it fills up with air bubbles.

I have some old coral and shells that I found on the beach when I lived close to the ocean.

I have rocks and shells mostly. And some aquatic plants.