Early English Books Online and the Text Creation Partnership has created a standardized XML/SGML encoded electronic text editions of early print books.  View the EEBO-TCP guide to learn more about the initiative.

From the EEBO website:

Following its first launch in 1998, EEBO now contains page images of virtually every work printed in England, Ireland, Scotland, Wales and British North America and works in English printed elsewhere from 1473–1700. More than 200 libraries worldwide have contributed.

Visualizing English Print - a member library inter-disciplinary project with Mellon Foundation funding.