The National Archives recently released records of the Watergate Special Prosecution Force, including transcripts of President Nixon's grand jury testimony of June 23-24, 1975. The records are available at the GPO's FDsys site and the Our Archives Wiki. Nixon's testimony begins at Folder 9/16. For background information, see the National Archives' press release.
Legal information and research resources from The Ohio State University's Michael E. Moritz Law Library