Here's some great footage of Miles Davis in concert in 1973, I love this period though it is (still!) widely derided by many jazz critics. There's loads of commentary out there of course. Here are a few samples: Julian Cope on early-1970s Miles, an overview of "The Electric Years" from Perfect Sound Forever, and a website Miles Beyond, related to Paul Tingen's book on Davis' post-1967 music. You can also watch the documentary Miles Electric: A Different Kind of Blue with musicians speaking about Davis' 1970 concert at the Isle of Wight, interspersed with concert clips.