After a brief introduction to Atlas Shrugged, this essay provides a very good overview of the alternative between altruism and egoism. While not a work of technical philosophy, it is substantial: it quotes philosophers and textbooks that explain the meaning of altruism and clearly differentiates what rational egoism means for one's life, versus what altruism means. It also generally outlines Ayn Rand's argument for life as the standard of value and for rational egoism.
Atlas Shrugged and Ayn Rand's Morality of Egoism by Craig Biddle
The book-length version can be found here: Loving Life: The Morality of Self-Interest and the Facts that Support It by Craig Biddle
Recommended technical works are here: Viable Values: A Study of Life as the Root and Reward of Morality and Ayn Rand's Normative Ethics: The Virtuous Egoist by Tara Smith