Hmm... both Messiah and Sakurai are usually at the graduate level. If you're fairly strong in math I'd recommend Messiah, but I can't recall off the top of my h

Hmm... both Messiah and Sakurai are usually at the graduate level. If you're fairly strong in math I'd recommend Messiah, but I can't recall off the top of my head whether there is a good chunk of physical knowledge expected. IIRC, it's a more axiomatic approach than most QM textbooks, so I'd pick this up (I believe Dover has a cheap version, but it's also available on PDF in most places). The usual undergraduate textbook that people recommend is Griffiths, though I definitely disagree with its usefulness (the book often opts for doing a bunch of calculations to 'get the intuition,' as opposed to explaining some points clearly, which is fine but I dislike this approach). If you're up for a fantastic, but quite dense, reading, Bohm's Quantum Theory holds a special place in my heart for its brilliant motivation and fairly clear exposition of foundational QM (note that it doesn't concern itself with the notion of Bohmian mechanics at all). This book sits on my bookshelf with hundreds of notes all over its pages. Of course, there is a good chunk of physics expected to be able to read this book, but you should skim it and skip to the chapters of interest as a good reference !