The Third Edition of Computer Systems: A Programmer's Perspective came out in March. The CS:APP web page now contains information for this edition, with a link to the web pages for the second edition. We already have a (fortunately small) errata page.
This fall, we will be teaching 15-213, the CMU course that inspired the book originally. Leading up to that, we will update the lecture slides and the labs, and we will be making that available on the instructors' site.