A weekend visit by out-of-town friends served as a welcomed reminder of how much fun it is to browse the Boston-Cambridge used bookstores. We didn't manage to visit all of them, but we spent quality time in four:
Brattle Book Shop on West Street is full of great finds, especially the $1-$3-$5 outdoor bargain stalls. This is my favorite used bookstore in the area.
Commonwealth Books adjoining the Old South Meeting House is a great little bookstore jam packed with books.