The Mickey Mouse Mini Speaker packs big sound into a small package. The mouse ears pack in a speaker powered by USB, although there is a rechargeable battery, if you want to go mobile with it. A 3.5 mm jack makes it compatible with pretty much any mobile device out there, so Mickey will play nice with whatever you’ve got.
The speaker is small enough to fit in your hand, which makes it worth a recommendation on its own – it’s a fairly powerful speaker, and the ease of transporting it is awfully nice. You can get a Mickey Mouse Mini Speaker straight from the source on the Disney Store for about $20.