The extremely cool NASA JPL video Triumph at Saturn (Part I) is really worth a watch and/or listen. (Don't forget Part II as well!)
26:30 it discusses Cassini's gravitational assists; first two at Venus then one at Earth:
...but the project's first priority was getting safely past the Earth, which occurred in the summer of 1999, giving Cassini another 12,000 miles per hour of speed.
Earth Flyby: August 18, 1999, Cassini Speed: 99,000 mph
Several deep space spacecraft have use gravitational assists at earth via close flyby's. I'm wondering:
Question: Which deep-space spacecraft flew closest by Earth during a gravitational assist.