There are almost as many wireless Bluetooth keyboards on the market as there are Bluetooth speakers. But why spend money on yet another keyboard for your mobile devices when there's probably already a perfectly good one on your laptop? With this Bluetooth USB transmitter dongle from Buffalo, the keyboards you already have can also work on your smartphone or tablet.
Using a small application that runs under OS X and Windows, you can choose to have your computer's keyboard work with your PC, or re-route every keystroke to a mobile device connected over Bluetooth instead. It's that easy, and for $43 it means you don't have to travel with a separate keyboard. And as an added bonus, your laptop's tilting display makes for a perfect smartphone stand when you're pounding out longer messages.
Of course, why anyone would actually need to type on their smartphone or tablet while their laptop is out and powered up is another question, so perhaps this is a solution still looking for a problem to solve—but it's still a neat trick. More here.