Apple is rumored to be releasing an iWatch. But if you can't wait, or find yourself using your iPhone to tell time instead of a watch, consider the iHangy ($19.99 and up).
The iHangy is a clever slip-in case and adaptor that lets you dangle your iPhone from the included keychain or necklace. Optional earbuds make it a pleasure to listen to your music. Their newer models even have a built in stylus.
It is a bit of a hassle to remove and reinsert your iPhone into the iHangy case, so you will probably want to keep it in the case, but that's not a bad thing. The case itself offers plenty of protection so you can use it independently from the hanging feature.
With the iHangy, you get a lot more than just a case, and can experience "Wearable Computing" today without waiting for an iWatch!