One is Ken Schwaber, who talked to them for about an hour, mostly about Scrum. The excellent video of his talk is here. The nuances of Scrum become clearer when you hear Ken explain it. His website is here.
Esther Derby and Diana Larsen also visited the Googleplex. Their talk about Agile Retrospectives is here. I am a fan. Of Agile Retrospectives (the activity and their book). And of Esther and Diana.
See also their blogs here and here.