In this concise article in the journal Nature from October 2015, Andrew Robinson reflects on the history of attempts to decipher the Harappan script. More than 500 distinct Indus symbols have so far been identified, and it is now generally believed that the script was read from right to left.
Coningham's article from an anthology of research on the archaeology of the Harappan Civilisation presents an overview of the complex nature of the origin and decipherment of the Indus script.
A well-illustrated 140 slide PDF that explores the Indus script, origins, writing direction and more. While the slides by Indus scholar Dennys Frenez lack his narration, many of the slides are self-explanatory and provide a rich visual overview of the Indus civilization its writing and the many issues involved.