To build a foundational understanding of quantum mechanics before tackling Merzbacher's text, several introductory books are recommended. Griffiths' "Introduction to Quantum Mechanics" is highlighted as the least challenging and a great starting point. Other suggested alternatives include McGervey, Liboff, and Cohen and Tannoudji, though the latter's layout may be less favorable for some readers. For a deeper mathematical perspective, von Neumann's "Die Mathematische Grundlagen der Quantenmechanik" is considered essential, along with J. Prugoveçki's "Quantum Mechanics in Hilbert Space." Messiah and Schiff are also noted as strong choices for more advanced study. Overall, starting with Griffiths is widely endorsed for beginners.