Some newer links I just added:
Phoenix Disassembler Only on version 0.5 at the moment, but a disassembler which is looking good so far.
PlanetBooks Free online books in just about every computer subject you could want to read about, at last view it had 680 books on there. An excellent resource, and will save you some money - so now you owe me :)
A few links which I took from my old site, but I will be updating this page shortly with some of my favourite places ;)
Decompilation Page Well worth a visit. This page contains links to many other disassemblers and to various technical resources on Disassembly and Decompilation.
Sandpile This is a good site for information on processor instructions, both documented and undocumented.
Ralf Browns Interrupt List A resource for the old DOS programmers, Ralf Browns interrupt list is the definitive guide to interrupts on the PC.
Wotsits File Formats Quite a few people have been asking about the format of the PE file. Wotsits file formats is a good place to start looking for information on file formats, and provides a good set of resources on all kinds of file formats.
www.MyFileFormats.com. I have actually removed the link to this site. They just blatantly copied the whole of the wotsit.org site and called it their own. Although all of the information is public domain it's something that just is not done. I urge you not to use this site, and to use Wotsits instead, a site which someone has put a lot of hard work and effort into providing good resources for programmers.
Intel Manuals for the Intel architecture manuals and detailed information on instructions,etc.
Free Compilers and SDK's for other resources.
Now for some alternative links ;)
Digicrime.com WARNING: this site can be dangerous to those with crap browsers and no sense of humour. Seriously though, this site managed to get itself blacklisted by McAfee which just goes to show that McAfee obviously do not have a sense of humour. Just don't hold me responsible if anything happens to you on this site ;)
Exploder WARNING: also banned by McAfee someone that highlighted the security problems of ActiveX. His ActiveX control, Exploder, performs a clean shutdown of Windows 95 from a web page, although running any program is theoretically possible. His FAQ makes very interesting reading and shows the power of big organisations in the modern corporate society. In fact it always seems strange to me that corporate America is so powerful and crushes small opposition and yet someone within those powerful corporations wields that power. Corporations do not make decisions, people make decisions. So corporations reflect the nature of people. McLain highlighted a security weakness in a responsible manner and was nearly flayed alive for doing so. Right ? Wrong ? You judge.
Happyhacker Wanna play ? Go and play with happyhacker who run servers especially for you to go and play with. Join in the wargames - there are even ways to win money :) Seriously though, I don't condone hacking, and people are always scanning me (so lame) which is really annoying. If you really want to play then go and play here, legally. You will get far more respect for it.