There are many excellent textbooks for introductory astronomy; the list below includes most of those that are currently in use, in no particular order. Maintaining a comprehensive list is nearly impossible, however, because publishers keep putting out new editions with different titles, authors, organizational plans, and abridgments.
The important thing to know is that all of these books are very good. The differences between them are mostly matters of personal taste. Some books are significantly longer than others, and hence more detailed in their coverage, but this isn't always an advantage. The continual revisions to these books are rarely of much consequence, so any edition published in the last ten years will be perfectly adequate for our course. You can therefore save a great deal of money by purchasing a used older edition through the internet.
There is, however, one serious potential pitfall: Most of these books are also available in two-volume versions, intended for two-semester course sequences. Typically, one volume covers the solar system while the other volume covers stars and galaxies. Our course will include all of these topics, so you should avoid buying these separate-volume books unless you obtain both volumes.
Another option: The following coffee-table book isn't really intended as a textbook, but it can still serve the purpose in most ways. It is a little weak on the more technical and quantitative aspects of astronomy, but it is much better than a textbook at describing and illustrating constellations, the solar system, and specific stars and deep-sky objects that you can observe with the naked eye or a small telescope. It is much less expensive than a new conventional textbook, but probably more expensive than some used older-edition textbooks: