harvard bookshop is simply one of the best shops around. With a large selection of well selected books and in a clean, well organized space, the shop makes browsing a pleasure. They specialize in current releases in all categories -- especially scholarly subjects such as philosophy, history, area studies, as well as literature, etc. In the bottom level, they have remainders (very good titles) and used books (which are pretty decent) -- though not nearly as good as Raven Used Books a few blocks away on John F. Kennedy Street. Actually, the two together, make going to Harvard Square for book buying the perfect location (not to mention the other 6 or so general and speciality shops in the square).
Pros: great new releases, clean and organized