If you have an older stereo system or speaker dock lying around that doesn't offer wireless streaming, a few companies make adapters that enable you to add Bluetooth to an existing set of powered speakers or an iPod speaker dock for not too much money. Logitech's version is the Wireless Speaker Adapter, while Belkin's is the Bluetooth Music Receiver (model F8Z492TTP) reviewed here.
The truth is there isn't much difference between the two in terms of what they do. But the Belkin is significantly smaller, about half the size, largely because it doesn't have a composite audio connection (red/white) built into it; it just has a 3.5mm minijack. And while the Logitech comes with a single 3.5mm-to-RCA cable, the Belkin includes that plus a 3.5mm-to-3.5mm cable. In other words, both of them can be connected to either type of audio input.
The Belkin Bluetooth Music Receiver looks like a shrunken-down version of an Apple TV or Roku streaming media box (or, if you prefer, a hockey puck). It has to be plugged into a wall socket to get its power, and the AC adapter is actually bigger than the unit itself.
As mentioned, the included cables offer maximum flexibility for connecting just about any powered audio device. You can plug the Belkin into any stereo, boom box, AV receiver, TV, or even an old pair of PC speakers -- anything with a free input. Because Bluetooth doesn't need line-of-sight with the audio source, you can even hide the Belkin box instead of having to keep it out in the open.
The audio source in question can be any Bluetooth-enabled smartphone (iPhone, Android, Windows Phone, BlackBerry), most tablets (yes on iPad, no on Nook Tablet and Kindle Fire), later versions of the iPod Touch, or many PCs, Macs, and laptops. Like the Logitech, the Belkin receiver features Bluetooth v2.0 with EDR and is compatible with all devices enabled with A2DP stereo Bluetooth. It remembers up to six paired devices.
Once you've connected the little box to your stereo's input with the included cable, you then just have to pair it with your Bluetooth-enabled device. While the Logitech adpater has a "connect" button that puts it into pairing mode, the Belkin simply makes itself available for pairing as soon as you plug it in. I was able to pair an iPhone 4S as well as an Android tablet without any trouble.