The Modern Model. This site requires a free registration (unlike FreeBookSpot), but it offers a mix of public domain works and exclusive self-published content. Be careful to avoid the "Premium" upsell.
The Spiritual Successor. ManyBooks looks and feels like what FreeBookSpot used to be. It aggregates free eBooks from around the web, filters them for quality, and offers them in multiple formats. They have a vast collection of indie author promotions and public domain texts. FreeBookSpot
The Directory. This site works very similarly to the old FreeBookSpot model: a clean directory linking you to free public domain eBooks and audiobooks. The Modern Model