From J Software, a new book J for C Programmers in PDF (zipped). Via LtU.
Oh, and in case you don't know what J is:
J is a modern, array oriented, high level, high performance, general purpose programming language. J is used in a variety of industries including banking, investment analysis, insurance, derivative trading, scientific research, and education.
I just checked out the What is J PDF. It seems like it's used for math and graphing a lot, but it seems like something like Mathematica would be even better for that. Is this comparison between the two justified?
Not that this will help clear matters up, but I found this paper interesting. It uses J to teach math.