As a programmer interested in category theory, I found this book a rather good balance between the abstract non-sense of CT and what I might actually use in programming. I wonder if anyone else has good books to recommend? I feel that the contents of the book remains a bit hard to appreciate in full unless you have ran into these concepts previously.
John Baez' recent work on Mathematics of Tuning Systems is such a fun read. I enjoy how he explains ideas so clearly that the general public can understand and appreciate.