1) ubuntulinux.org - This is the official site of Ubuntu Linux. All Ubuntu enthusiasts should make this the starting point of their journey towards embracing Ubuntu. On this site, you can get the latest official news related to this project, place orders for your free Ubuntu Cd's and search or browse for a particular package for your version of Ubuntu among other things.
2) help.ubuntu.com - This is the official documentation site for Ubuntu Linux developed and maintained by the Ubuntu documentation project. This is the first place any Ubuntu user must go to get his problem solved. While you are here, do not forget to visit the FAQ Section on this site.
3) wiki.ubuntu.com - This is a part of the official Ubuntu project and as you can see is a wiki. A wiki can be edited by anybody a good example of a wiki being the wikipedia project. On the Ubuntu wiki, you can get a wealth of information about configuring this distribution. First time visitors to this site may be interested in checking the Help Contents page. A section which is specially interesting is the Restricted Formats section which gives tips on getting support for proprietary file formats in Ubuntu.
4) ubuntuforums.org - This is a high traffic web forum where you can post queries you have and get your doubts clarified. You need to first register to post in this forum. But just searching this forum will throw up a wealth of information a.k.a the issues that others faced and the solutions to these issues.
5) ubuntuguide.org - This guide is not affiliated with the official Ubuntu project but claims to be an unofficial FAQ where you can find solutions to getting your problems solved in Ubuntu. This site takes a How-To approach in giving the answers. Though recently, this site has become a bit outdated as I ran into some problem while configuring Ubuntu Breezy according to their directions. Nevertheless a very good site.
6) doc.gwos.org - This is a site which hosts the documentation for all flavours of Ubuntu. This site is maintained by the ubuntuforumn.org guys themselves and contains information in a more structured format. One page which might interest the Ubuntu users while on this site could be the Hardware Compatibility Guide.
7) Ubuntu Blog - This is a very good blog maintained by a Ubuntu enthusiast and as the name of the blog indicates, exclusively caters to all things related to the Ubuntu distribution. Here you can get latest news, links to popular sites and experiences of the blog author in getting things done in Ubuntu Linux.
8) fridge.ubuntu.com - This site claims to be an information hub for the Ubuntu community bringing together news, grassroots marketing, advocacy, team collaboration, and great original content. This is a site you can enter in your watch list if you are interested in knowing about the happenings in the Ubuntu world.
Automate all the Ubuntu housekeeping tasks
The next two sites list scripts which can be downloaded and used on your system to get support for a lot of proprietary features in Ubuntu without any (or very little ) user intervention.
9) Automatix - This is a script which can be used to get mp3, wmv, quick time, encrypted DVD support and more on Ubuntu and all this as the name indicates rather automatically. All the user has to do is run the script. Unfortunately, this project is not supported any longer but the users can still download the script and use it. << NO USAR AUTOMATIX
10) Easy Breezy - On this site you can get another script which helps in automating the tasks of getting proprietary file support in Ubuntu Breezy v5.10. The author claims it to be a safer alternative to another well known project.