I always had a USB cable laying around and an iPod Touch (1st gen) or iPhone 3G attached to it. A couple of times I had an iPod hanging from the cable a couple of centimeters from the floor instead of lying on the desk. This started to bother me more and more so I bought an iPod dock from the Apple webstore.
The dock comes with a number of "adapters" for most of the recent (say last 5 years or so) iPods and iPhones. Since I own both an iPhone and an iPod Touch I'd be needing to switch adapters every time I "plugged" in a different iP*. The solution is simple, the iPhone fits the iPod Touch adapter (nr. 14) pretty good.