Many hotel rooms now have clock radios with an Apple Dock connector for your iPhone or iPod. However, Apple abandoned the Dock connector for the Lightning connector in its new iPods, iPhones, and iPads released this fall, so you may want Apple's Lightning adapter if you have a new Apple device. That adapter may not fit in all cradles and Dock-equipped accessories, so you may also want Apple's Lightning-to-Dock cable.
Note that these adapters don't work with specialty add-ons, such as for video-out, MIDI, and even iPod control. They're solely for charging and data transfer.