This site makes freely available the best-quality digital audio and selected transcripts for people who can not go to the NARA's Archives II facility in College Park, Maryland, or to the Nixon Presidential Library in Yorba Linda, California. It also makes "the NARA-created tape logs (summaries of conversations), time codes, the president's daily diary, as well as pertinent information about each conversation that makes your listening experience better and to make the collection more accessible."
This is an online exhibit from the Harry Ransom Center at the University of Texas, Austin. The papers were purchased in 2003 and are housed at the Ransom Center.
Some documents are available digitally through the exhibit site.