Downloading Debian

Disclaimer

This is intended to be merely a guide on obtaining the Debian GNU/Linux Operating System installation files, written by a Debian user, for (future) Debian users. It is by no means intended to replace the guides written by the Debian crew, nor it claims to be a better one. It's simply a longer story told short.
Also, I do not guarantee that, following this guide, you'll be able to download what you want, as the location and the structure of the Debian download servers may change at their own discretion. However, I'll try to keep up to date this document each time something new comes up.

Introduction

First of all, the official links:

Debian's main page: http://www.debian.org/
About Debian: http://www.debian.org/intro/about
Debian News: http://www.debian.org/News/
Debian official documentation: http://www.debian.org/doc/
Debian FAQ: http://www.debian.org/doc/manuals/debian-faq/index.en.html
Is Debian free? http://www.debian.org/social_contract#guidelines

Next, a few words about Debian distributions. Currently, the Debian Operating System is available in three versions: stable, testing and unstable (more info). Actually, the stable version is the one that eventually gets released, while the other two are the so-called "development branches", representing stages in the evolution of the OS. Something on each of them:

stable: indeed as stable as it gets, with thoroughly tested packages, but at the price of being somewhat outdated by many's standards. This version, once released, only gets security updates, nothing else. Perfect for servers, where stability matters most.(more info)
testing: this version is made up of software that has not been fully tested, but tested enough to ensure a low risk of breaking things. The stable releases must pass through this stage first. While it gets a lot of updates almost daily, it's stable enough (as many of the Debian users say) to choose it as your desktop distribution. Keep in mind though that testing is a transitional version to the next stable release. (more info)
unstable: this is the "foundation" of the Debian OS, its "stem" if you like. All the software that will eventually make its way to the stable version, is first uploaded here, tested for a while and, if it gets green light, it moves on to testing for...more testing. This version will always be the cutting-edge of Debian software, but you get no guarantees that something won't break in the middle of...whatever you consider most important. Some say it's safe enough to use as a desktop system, others say that it breaks sometimes but it gets fixed quickly and others would strongly advise against using it unless you are a developer/tester that is willing to send feedback to the Debian crew. Believe whomever you want. (more info)

I won't give details here, but there are also two more versions, one called frozen, which is a stage between testing and stable and the other experimental, which comes before unstable.

Other links that may clarify what I've said so far:
http://www.debian.org/doc/manuals/reference/ch-system.en.html#s-dists
http://www.debian.org/doc/manuals/debian-faq/ch-ftparchives.en.html#s-dists
http://www.debian.org/doc/manuals/project-history/index.en.html

Which is which?

Besides being called stable, testing and unstable, the Debian distributions are each assigned the name of some fictional character from Pixar's Toy Story (so far). Thus, at the moment this was written, the stable release was codenamed Sarge (also known as 3.1 rev.0), the testing version name was Etch while unstable is always codenamed Sid. (more info)
Long things short, it's up to you which distribution you choose. I (*emphasizing personal opinion*) recommend most of you to go with the testing distribution. This way you get a stable enough system and *almost* up-to-date software. I won't recommend unstable here, because, even if I'd want to, you can't download it. The only way is to download one of the first two versions and upgrade later.

Ways of downloading and installing

Ok, once you made up your mind, you must know there are several ways of downloading a Debian distribution: via jigdo, http, ftp or BitTorrent (more info). You must also know that there are several ways of installing it, as well: from a CD (or DVD) set exclusively, by using the first CD in a set or by using a special image, called net-install.

To help you decide which way to go, I will point out some things:

if you install from a CD set exclusively, the installation will be, obviously, as fast as your computer can handle it. Also, if you need to reinstall, you already have the data. On the other hand, you have to download first a whole bunch of CDs: currently, the stable distribution (Sarge) is 14 CDs. Multiply that by an average 640 MB. Or, if you prefer, it's 2 x 4 .1 GB DVDs.
the first CD in a set should be enough for most of you, as it contains the installation system and the most popular packages. The software on the next CDs is sorted in order by popularity. So you must download only around 650 MB but there are however chances that you might miss some package you desperately want.
currently, the net-install option seems to be the most popular one. You download only one, ~100 MB ISO file, which contains only the base system. Once installed, it will fetch the rest of the packages you need by FTP or HTTP. If you have a decent Internet connection speed this is what I warmly recommend. Even if you have a slower connection, you're not forced to download everything at a time.

A most important thing to note is that you may take advantage of the latest packages in testing or unstable even if you use stable. Also, you may use a first CD from the stable version to install, then upgrade to unstable if you like. Or use a "testing" net-installer then get packages from stable only. All this can be done by just changing a few lines in a file. See the links at the end of the file for more information.

Note: there is actually a netinstall image for Sid, but it will download the packages from testing unless specified otherwise, thing that you can do with the netinstaller for the other versions.

The links

And now comes the most important part of this document, the actual download links. I want to remember you that, at the moment, the stable distribution is named Sarge, while Etch is the testing one.

FTP/HTTP:
- Stable:
  - Debian primary CD image server:
  - Mirrors: click here, then descend into "/current", then pick your architecture and then choose "/iso-cd" or"/iso-dvd", whichever you like.
- Testing:
BitTorrent: (more info)
- Testing Desktop Choice cd1:
  - There are now three different Etch CD1, you can now pick the one with the Desktop you want:
    One gives you GNOME, one gives you KDE and one gives you XFCE. It's just a matter of downloading the one with the desktop you want.
- Testing:
  - CD set
Jigdo: you'd better read all this stuff to decide whether you want to go with jigdo or not.

Note: Due to a bug discovered in the 3.1_r0 images, they were fixed and renamed as 3.1_r0a. You may still use a 3.1_r0 image if you downloaded one, additionally you should do what is written in the Note placed at the beginning of this page.

Note: most of the links above refer directly to the images for the i386 architecture because it's the most popular. If you have something else than a i386, take a look at where are you located at the moment (on the page or in the address bar), go up one directory (or two, depending on the situation) by clicking on "Parent directory" link, pick the one you need, and descend back to the corresponding folder.

Note: Some of the mirrors do not provide images for all the architectures. Also, some architectures do not have the images for a certain type of files: some don't have DVD ISO files, others don't have BitTorrent files, etc.

Note: You may find other mirrors as well in places such as LinuxQuestions ISO or The Linux Mirror project.

Well, it's time to go get them!

Links for further reading and for getting help