Quadcammer

pretty simple.

Buy a small (i think they are 32oz) bottle of propane with a valve on it to control the flow (the torch tip helps to positively locate the flow of gas).

Open the valve a good bit and move it around the engine bay. If there is a cracked/unattached hose, when the propane gets into the hole/opening, the engine will rev up a bit. Its not foolproof but a pretty quick and dirty way of determining whats up.

Some shops have smoke machines they can hook up to the intake to identify vac leaks.

Turbodan

party stores sell the smoke machines for about $10.