Griffin has announced an accessory called Twenty, a small audio amplifier that will accept audio from an AirPort Express to drive unpowered speakers. The Twenty includes a TOSLINK cable to deliver pure digital audio from the AirPort Express to the unit, and additional connectors in the back allow you to plug speakers right in.
As the name implies, Twenty delivers 20 watts per channel of 2.1 audio. The unit's top includes a nifty and well-thought-out adapter that allows you to plug your AirPort Express's power plug directly into it, which means you'll only need one outlet to power both the AirPort Express and the Twenty.
Audio can stream from your Mac or iOS device to the AirPort Express via AirPlay, and from there audio passes from the AirPort Express directly into the Twenty. As helpfully noted on Griffin's website, you'll have to purchase your own AirPort Express and speakers.
Griffin's Twenty looks like a nice, miniaturized replacement for a full-fledged audio amplifier. I've already got one AirPort Express in my living room tied directly into my 7.2 surround sound system, but Griffin's Twenty would be ideal for the secondary AirPort Express in my office.
Griffin hasn't released pricing or availability info yet, but if you're interested you can sign up for e-mail alerts on Griffin's site.