There are monographs, collected books of papers, and textbooks. Monographs have some prestige, but most have small readership and small impact; some Ph.D. dissertations are published as monographs, especially in Europe. Books that are a collection of papers are often used as a way of promoting research in a new area, or getting around the publication delays of journals. Collections of papers are also used to reprint and archive important papers that were originally published in hard-to-find places. The first good textbook in a given area generally has high impact, though writing just another textbook on a well covered subject does not.
The respected presses for books are generally the same as those for journals. For example, Springer also publishes two respected series of books, the Lecture Notes in Computer Science, and the Texts and Monographs in Computer Science.