Deb of Dhamma Matters wrote an interesting blog about Sri Nisargadatta Maharaj. He wrote a book called I Am That That, which is recommended by Jack Kornfield. Kornfield is a leading Buddhist teacher, and a former monk that practiced under Ajahn Chah in Thailand. It’s a compilation of questions and answers between Sri Nisargadatta Maharaj and his students.
There’s also a link to an interesting video about Sri Nisargadatta Maharaj, who was a lay householder and shopkeeper in Bombay that developed some interesting insights.
I particularly like his quote, saying that the “Greatest guru is the inner self.” This is similar to what Lama Zopa Rinpoche says. In his book the Heart of the Path, he says the real guru is the inner guru.