The judicious use of props can add much to just about any game by drawing the players into the story. It's so easy to say things like, "I hide the Renoir behind my back," or, "I gather up all of the spilled diamonds," or, "I defuse the bomb," that players will frequently utter things like this without thinking about what's involved in such an undertaking.
But give the player something tangible that represents a Renoir painting or the triggering mechanism for a bomb, and now he has to think about what he's doing with it.
There are times, though, when props are not recommended. Never use a prop if doing so would jeopardize the safety of your players or those around them. Props with high mess potential should also be avoided. And props inherently slow things down, so if you want a scene to be resolved with lightning speed, you might want to handle that just through narration.
Here's my current list of offerings. Things with the 
symbol are available now; the rest are things to
come.