RadTech 13-860 ProCable Shortz Dock Extender for iPhone, iPod and iPad - Black
This item simply does exactly what it says it will do. I have docking stations for my iPads, my daughter's iPhone 3 and itouch and my iPhone 4.  The iPads (1st gen) are in the original apple case and they fit great on the radtech extender and the remaining devices listed above are all in otter boxes and the radtech works great with them.  I have a Bose system, 2 philips systems and 2 RSA systems (docking stations/mp3 players) and they are all interchangeable now with all my different apple devices.      One