I recently finished an interesting book by Sophy Burnham entitled The Ecstatic Journey: Walking the Mystical Path in Everyday Life. She is the author of A Book of Angels, which I have not read, but was well-received and sounds significant. Perhaps sometime in the future.
In The Ecstatic Journey, Burnham recounts her trip to Machu Picchu in Peru where she had a profound mystical experience. It shook her to her core, and the ripples of the event caused her to question nearly everything in her life. Over the course of time, she felt compelled to study the experiences of other mystics, and these stories are interspersed with her own story throughout the book. For both the personal and historical view of mystical experiences, this is a good book to read.
What I really liked about her writing is that she made these experiences -- so often nearly impossible to capture into words -- accessible. If you have ever tried to read William James' The Varieties of Religious Experience, you will know how valuable an ability that is.
If you are mystically bent, or have questions about what others have experienced, this is a great resource. If you find all this talk too "woo-woo" for your taste, then it's best to skip it.