With a plethora of independent bookstores in this student run city, and half the literati living around town, Harvard Book Store (not to be confused with Harvard University's bookstore across the way) singles itself out by having the most all-consuming variety of literary and academic books around. Further, a killer reading series each year.
With a floor of new books (many of which are signed by local writers and academics) and a basement of used books (used by local student and professorial geniuses...), true readers cannot exit empty handed. Particularly for intellectuals, you'd be hard-pressed to find another store with so many books of critical and cultural theory at the ready.
The used poetry section is absurdly top-notch and magical at all times.