Here is my list, which is biased towards Linux. Almost all the books mentioned here are dated and primarily written for 2.6 based kernels. Although many concepts are still applicable and in certain subsystems, the code will be as is with minor changes. So, despite them being old they are still good references.

* Design and implementation of the FreeBSD operating system: Good and thorough deep dive in FreeBSD OS. Must have.

* FreeBSD Device Drivers: A Guide for the Intrepid: Didn't quite read it all but looks fine for FreeBSD.

* Mac OSX internals - a systems approach by Amit Singh: It was good back in days but now outdated.

* Linux Device Drivers, 3ed : Very dated but still good to grasp Linux device drivers in general. The code examples are bit silly but good enough. There are some GitHub repos which have updated code for latest kernels.

* Essential Linux Device Drivers by S Venkateswaran: It complements LDD3 book quite nicely. Has some real device examples and very exhaustive. Must have.

* Linux kernel development by Robert Love: Very good for short/quick intro. Best for preparing before interviews ;)

* Professional Linux kernel architecture by Wolfgang Mauerer: As other book, its dated but some of the explanations about interrupts, PCI, etc are good. His callgraph approach was very handy in understanding things.

* The Linux programming interface by Michael Kerrisk: Not really about OS but next thing close to it - system programming (the real system programming). Must have.

* Understanding Linux virtual memory manager by Mel Gorman: As other books, it's dated but still one of the best available to get a handle on memory management under Linux. Must have.

* Understanding the Linux kernel: Dated but still my go to book to refresh certain subsystems. Must have.

* Linux Kernel Programming by Michael Beck: Mentioned for historical reasons, else most out dated book here (2.4 based). Horrible editing and English but heck! I loved it back in the days :)

* Linux kernel networking by Rami Rosen: Never read it but quite dated.

* Understanding Linux network internals by Christian Benvenuti: A real bible of Linux networking. If nothing else, your jaw drops at the effort author made to write this book. Dated but unlike more generic Linux kernel things, network stack is still same in its core. Must have.

* The Linux kernel primer: A top-down approach for x86 and PowerPC Architecture: Very dated book but good to read from PPC perspective. Lot of things have changed since its publication.

* See MIPS Run by Dominic Sweetman: dated but gives good idea about MIPS internals and how Linux uses it.

* IA-64 Linux Kernel: Design and Implementation: Its dated not just w.r.t code but also w.r.t. hardware. Nonetheless, it gives a good insight into IA-64 architecture and Linux from non-x86 perspective.

* Definitive guide to Xen hypervisor: this is the only book on virtual machine which is not just from user perspective. While best way to learn VM is through reading architecture spec and code, this book still satisfied me w.r.t. virtual machine internals.

Every other book on amazon about Linux kernel is more or less useless. For more academic book, "Operating systems - three easy pieces" is good.