Some links that I have found interesting

Linux device drivers: A really awesome book that is both friendly, detailed and hands-on.
NASM manual: NASM (or Netwide ASseMbler) is a freely available assembler that is rich in features and not difficult to learn. This is the manual that you will find indispensible while working with NASM. However, this is somewhat nerdy, and is by no means a tutorial to teach you assembly language programming.
Free e-books from Abacci: Plenty of free (and not free) e-books in MS-ebook format. In particular, I got a free copy of one of my favourite books by Conan Doyle here: Round the Red Lamp Stories.
Project Gutenberg: A HUGE database of free ebooks.
Works of Kafka: Works of Franz Kafka. Both in German and in English.
Redhat Linux 6 Unleashed: A book on Linux. I have not gone through the book carefully. But based on my cursory perusals it looks promising.
PID control: Pretty detailed site about the practical aspects of PID controllers.

Postscript 2 reference: Just what the name suggests. It has description of all the standard Postscript functions, commands etc in a browsable format. It is not a tutorial.
ShockWaveFlash (SWF) file format details: Impressive details that I could not find elsewhere.
Intel architecture software developers' manuals: There are 4 volumes. All are available online as HUGE pdf files. You may also request Intel to send you free copies of the printed book. They sent volume 1 to me totally free of charge (not even shipping charge!)
Interrupt jump table: A huge database listing the BIOS and DOS interrupts of an IBM PC.

Javascript image preloading: Some advanced techniques of javascript.
Controlling the real world with computers: Looks like a pretty informative page.
Making animated gif: Good tutorial.
CVonline: Very good starting point for image processing algorithms. Non-mathematical.
How things work: A SUPERB site that describes how "things" work, where "things" ranges from computer to credit card to the united nations.
Making your own toy boot floopy (Part 1): The first of three very nice articles.
Making your own toy boot floopy (Part 2): The second in the series.
Making your own toy boot floopy (Part 3): The third one.
Virus writing guide: Pastime for the mischievous nerds!
VGA mode 13h graphics: Some useful things.
Interesting codes in assembly language: Good examples.
Data acquisition and control systems using Linux: Looks very promising. I am yet to go through it in details.

Music theory tutorial: A FABULOUS site with flash tutorials on music theory!
Bengali songs from Calcuttaweb: Plenty of nice songs. Links to simlar pages are provided.
Western classical: A vast database of western classical music. Browsable, searchable. However, the sound quality is poor compared to what you get from a CD.

Optical illusions: Lots of cute, little optical illusions.
A javascript game based on Shakespeare's Hamlet: A nice adventure game based on Shakespeare's characters. The game engine is written in javascript and is an excellent one.
Java games: Lots of java games, and some flash ones. In particular, I like the Wiz3 game. It has some really well-rendered animation.
POVRay: A free software package for ray tracing. A gem of a software!