For a heavy or sudden fall:
* Thumped
* Dropped
* Splatted
* Plunked
* Flopped
* Slammed
For a casual or relaxed placement:
* Set
* Placed
* Put
* Laid
* Positioned
For a sound:
* Thudded
* Bopped
* Plop (the sound itself)
The best synonym will depend on the specific situation and the feeling you want to convey.