Internet History Sourcebooks Project
Fordham University: Modern History Sourcebook: The Praise of Folly
This site from the Fordham University and the Modern History Sourcebook provides Erasmus' "The Praise of Folly" translated into English.
Other
Sheffield Hallam: Utopia as Mirror for a Life and Times
A great online article from Sheffield Hallam University. Excellent to read along with Utopia, or perhaps after an initial read.