Compass Designs has an excellent collection of tutorial articles. They are well organized, and well written.
And you would expect this to be so since the staff there are authors of several Joomla user's guide. Plus, he has a more comprehensive user's guide for sale on his site. Visit them at the Compass Designs tutorials here.
Well known template provider RocketTheme also has a a good selection of Joomla tutorials on their site. Some are specific to their template, but many are good overviews of Joomla in general.
Siteground is a Joomla friendly web hosting service that offers a number of very helpful Joomla resources. These step by step articles are quite helpful.