The Kensington accessory adapter for iPod shuffle:

“Get more out of your iPod® shuffle! The Adapter for iPod Shuffle plugs into the USB connector on your iPod shuffle and lets you play your music or charge your shuffle through many iPod-compatible accessories. From docking stations and chargers to FM devices and speaker systems, the Adapter for iPod Shuffle lets you get maximum entertainment from your iPod shuffle.”

iLounge reviews Kensington’s accessory adapter, and gives it a general recommendation: “As with most of these accessory adapters, what you’ll get for $20 is a fair compromise - a way to make a reasonable number of standard iPod speaker, car, and charging accessories compatible with the cheapest iPod. In our view, it’s quick and semi-dirty, but probably a smarter buy for shuffle owners than going out and getting shuffle-specific accessories at this stage of the low-end iPod’s life.”

Source.