For people who are looking for a less permanent option to listen to music in the shower, a few varieties of wireless shower speakers are available. The wireless version usually consists of some portable speakers encased in a waterproof housing that can be place anywhere in the shower. Some models may have a hook to hang from the shower faucet.
The wireless shower speakers pick up their signal from a stereo that stays outside of the shower. It may be a standalone unit, or it may be one that can dock with your iPod or portable music player. Regardless, the general concept is the same: The stereo remains outside of the shower where it is dry, and the speakers can be brought into the shower (or pool, etc.).
There is another variant of this, and that is a one-piece waterproof stereo. These are technically considered wireless shower speakers by some companies, and but more accurate description would be waterproof stereo. Imagine a clock radio, or portable CD player, or one-piece iPod dock where the entire unit is water proof and you can bring it in the shower with you. It’s basically like that.
Wireless versions are best for people who are looking for a portable option, such as people in apartments who cannot do the required construction to actually mount flat speakers in the shower.