Japan's WellTone has a new USB Skype handset coming out which may or may not contain a version of Skype in its internal 64MB of memory. The uncertainty lies in how the company is yet to receive permission from Skype to include their software. Other than that, the "Skype USB Handyphone (WB-2001)" is your standard for a USB handset.
Press Release [WellTone via AV Watch]