Preview at WWDC likely in June, followed by September launch.
Apple's Lightning to 30-Pin Adapter Begins Shipping
Apple is offering two versions of the adapter, a $29 direct plug adapter and a $39 adapter with a short cable. The adapters allow users to connect their new Lightning-enabled devices such as the iPhone 5 and forthcoming iPod touch and iPod nano models to docks and other accessories designed for the previous 30-pin dock connector.
(Thanks, MudgeeMac and Daniel!)