Props are great in moderation. My friend has these fantastic looking dungeon walls, doors and all the other decorations, but it takes a long to set up. Because these things are costly he doesn't have many so he needs to tear down where we just were to build the next section. The other thing it you can't bump the table or the walls come tumbling down. A dry graph.hex map with dry erase markers are much better. Quick and easy to use. Keeps the game flowing where as when he has to rebuild the walls its like waiting for a commercial to end.

Hand outs are always cool. Using bags of pennies or dimes to toss on the table to represent the reward is always a nice touch. The one thing I like to do a fantasy billboard.

Since I primarily play in medieval fantasy games I imagine there are a ton more props you could use for a modern game type setting without bogging down the game.