Ramana MaharshiSages, the Knowers of the Truth, declare that the destruction of all mental activities [chitta-vrittis] is alone the greatest Happiness. Therefore desirelessness, which is devoid of both likes and dislikes, is the best means.

Ramana Maharshi

Tattva Bodha
Knowledge of Reality, by Śaṅkarāchārya

Tattva Bodha Reference Materials:

Video/Audio Lectures

Swami Paramarthananda
36 classes (~30 - 55 mins each) 1, 2

Swami Anubhavananda
7 classes (~75 mins each)

Tattvabodha English 2 of 7 @ Prem Puri 2012

Swami Sarveshananda
27 classes (~45 - 60 mins each)

Swami Swatmananda
22 classes (~60 - 90 mins each)

02 Vedanta Fundas - Tattvabodh introduction-02

Swami Narasimhananda
12 classes (~60 - 90 mins each)

Introduction to Vedanta Tattvabodha Narasimhananda 2

Swami Viditatmananda
9 classes (search for "Tattvabodha" on the linked page)