In Marco Arment’s review of the Jawbone Big Jambox, he mentions that he mostly uses the $300 battery-powered Bluetooth speaker to listen to podcasts in the shower.
I would like to mention a $40 product that I think does a pretty good job at this, and that has many other uses as well: the Grace Digital Eco Extreme. (Terrible name. The company is Grace Digital. I suppose the “Eco Extreme” is because you can take it outdoors and do extreme sports near it.)
This is a rugged, AA-powered speaker/watertight case for your phone or music player. You put your phone in the case, attach the audio jack, and seal it up. You can take it right with you into the shower, and take it with you back into your bedroom when you get dressed. You can also use it as a mini boombox at the beach, doing yard work, etc. There is a little carabiner that you can clip to things. The phone itself can be held in place by a little mesh net inside the case if you like; I usually don’t bother.
In my opinion, this is a simpler, more practical, and more versatile solution than using bluetooth and a speaker that you need to charge. Also it’s much cheaper.
I have used mine every day for about two years, taking it into the shower each day, with no problems. Obviously I set it on a little ledge; I don’t know how well it would work being drenched. But a little water is okay. I have to change the batteries every two months or so.
Also: I like that it only has one speaker. “Stereo” speakers without sufficient physical separation between them are pointless and would probably drain the battery faster.