A couple of months ago I made the switch from Windows to Linux, and I doubt I will ever look back. Sure, sometimes business endeavors force you to use Windows applications, but other than that Linux gets the job perfectly done.
If you are considering to migrate to Linux as well, or if you have already been using it for a while but want to improve your knowledge, you might want to check the free Linux eBooks library on Homelinux.org.
You will find pretty much everything you need, from tuning the performance to shell scripts and kernel programming. Below you will find my favorite ones: