In Depth Tutorials
Introduction : Installing Ogre
Xorekis' Tutorial Pack : An old collection of Tutorials for begginers.
Mad Marx Tutorials
Tutorial series for Ogre 1.7.x using a minimal NeHe-like style with lots of code comments.
Beyond the Tutorials
Once you've finished the tutorials you can begin reading through the Cookbook for further examples of using Ogre.
Ogre Manual: The OGRE Manual:
PyOgre Tutorials: Ogre with Python
OgreDotNet Tutorials: Ogre with the .Net languages
MOGRE Tutorials: Basic level tutorials for MOGRE, an advanced .NET wrapper for OGRE
Recommended reading: OGRE Team and Users recommended programming-related books.