Article:
D&D 4th ed: The Slightly Moving Rod and other Malfunctioning items.

Contrary to popular belief, 4th edition is not all about combat, and not all magic items are focused solely on kicking down doors and causing a very bad day for the local evil doers.
Have you noticed that the Immovable Rod has been promoted from a 5ooo gp wondrous item to a 13000 gp item? That is most likely because the things are lethal in the hands of a clever role player.
For example, try fixing a dagger to the end of an Immovable Rod, goad some monster into chasing you down a corridor, and then with a minor action as you run for it, set the Immovable Shaft (as they are now known) and carry on.. is the beast likely to see the thing waiting in mid-air for it as it charges forwards?
So, seeing as the Immovable Shaft is such a handy item, but 12th level is quite high, you might want to give your players a knock off version, something an apprentice artificer slapped together as a summer project (and probably got a note to see the instructor after class).
Of course, the players have don't know for sure that item doesn't work quite as it should, but at that price, you would have to be careful right?

The Slightly Moving Rod is a level 5 Wondrous Item, it has a market price of 1000 gp.
Power (At-Will): Minor Action. Place the Slightly Moving Rod into it's position. It remains in place. It can be repositioned as another minor action if using the button located on it's end, otherwise any force applied to it will see it slowly move at a maximum of one square per round, in the direction it is forced. If the force exceeds 4000 lb (1.8 metric tons), the rod will suddenly fail and completely release, as though the button had been pushed to switch it off.

Next on the list is the adventurers little friend, the famous Bag of Holding, a handy means of transporting large quantities of equipment and loot, without all the book work of encumbrance.