Samsung just listed on their website a USB Host Adapter for the Galaxy Tab 10.1. This is the add-on device that may make your tablet look bulkier, but adds a slew of additional inter-connectivity options that really enhance the capabilities of the device. The adapter effectively upgrades the tab's 30-pin connector to full USB providing access to any USB device that is supported by the Android OS. Sadly, the adapter is already in the "back order" status as it sold out very quickly. More than likely we will see it restocked pretty quickly.
Source: GalaxyTabForums.net via Engadget and Samsung