My favorite by far is Geometry: A Guided Inquiry by Chakerian, Crabill and Stein. This is the book that had the greatest impact on my approach to teaching high school math. It came out in the 1970's, I believe, but was far ahead of its time. Among the things I learned from it:
- There are many benefits to organizing the classroom into cooperative groups of four
- Problems need not be ordered from easiest to most difficult
- Chapters need not be ordered according to tradition
- Inquiry and proof are not mutually exclusive
- Writing a paragraph is a more important skill than writing a two-column proof
- and more...
Finally, my own Geometry Labs is a good complement to any geometry text, offering discussion-sparking, hands-on activities on many geometry topics. (Where to get it.)
More on geometry.