I object to the site's notion that there is a "best" intro book in many areas, but I'd like to see listed on the site:
Griffiths' _Introduction to Quantum Mechanics_ is quite commonly used, even though it's a bit calculation-heavy. Beyond that or for more theory, perhaps Ballentine, or Dirac's original monograph, although neither is a very common text (if that's what someone's looking for, then Shankar [mid-level-ish], Cohen-Tannoudji, or Sakurai); Ballentine because it's new (relatively... 1998), and Dirac because it's old and it's what a lot of the mid-to-late 20th-century physics giants started from. Feynman's Quantum Mechanics and Path Integrals is also a no-brainer because it's been republished and it's now a $12 Dover edition.
Griffiths' _Introduction to Quantum Mechanics_ is quite commonly used, even though it's a bit calculation-heavy. Beyond that or for more theory, perhaps Ballentine, or Dirac's original monograph, although neither is a very common text (if that's what someone's looking for, then Shankar [mid-level-ish], Cohen-Tannoudji, or Sakurai); Ballentine because it's new (relatively... 1998), and Dirac because it's old and it's what a lot of the mid-to-late 20th-century physics giants started from. Feynman's Quantum Mechanics and Path Integrals is also a no-brainer because it's been republished and it's now a $12 Dover edition.