JSON
Javascript Object Notation
Developed by Douglas Crockford, of Javascript: The Good Parts fame
Hip alternative to XML for data sharing.
Example: http://www.archive.org/details/uso20110129?output=json
Some browsers automatically recognize JSON and provide helpful formatting. If not, there's probably a plugin to do that.
Command-line
jq is a nice command-line tool for JSON parsing on the command-line.