I just posted an Eagle library for XMEGA microcontrollers as a tool download. The library contains parts for the A1, A3, A3B, and A4 devices with the commonly used TQFP and MLF packages.
The BGA style packages are not yet supported as I felt these packages are unlikely to be required by people who use Eagle. Let me know if anyone has these Eagle packages already and I can add them to the library.
Based on people's comments on this thread, I will update the library as appropriate. Once stabilized I will send to CadSoft for inclusion on their download site.