Here is a script of user Telchar, which shows how to create an outline around a character, which works without shaders.

Screenshot of this effect, used in the game Torchlight:

material some/random/material/with/rim/effect
{
   technique
   {
      pass
      {
         texture_unit
         {
            texture yourtexturehere.png
         }

         //rim lighting
         texture_unit
         {
            cubic_texture rim.dds combinedUVW
            tex_address_mode clamp
            colour_op_ex add src_texture src_current
            colour_op_multipass_fallback one one
            env_map cubic_normal
         }
      }
   }
}

Here is the c++ code to do the same:

/*
    rim lighting
    see: http://www.ogre3d.org/tikiwiki/Create+outline+around+a+character

*/
#pragma once

#include <Ogre/OgreEntity.h>
#include <Ogre/OgreSubEntity.h>
#include <Ogre/OgreSubMesh.h>
#include <Ogre/OgreString.h>
#include <Ogre/OgreMaterial.h>


/*
    add the rim lighting effect to an entity.
*/
void highlight (Ogre::Entity* entity)
{
    unsigned short count = entity->getNumSubEntities();
    
    const Ogre::String file_name = "rim.dds";
    const Ogre::String rim_material_name = "_rim";

    for (unsigned short i = 0; i < count; ++i)
    {
        Ogre::SubEntity* subentity = entity->getSubEntity (i);
        
        const Ogre::String& old_material_name = subentity->getMaterialName();
        Ogre::String new_material_name = old_material_name + rim_material_name;

        Ogre::MaterialPtr new_material = MaterialManager::getSingleton().getByName (new_material_name);
        
        if (new_material.isNull())
        {
            MaterialPtr old_material = MaterialManager::getSingleton().getByName (old_material_name);
            new_material = old_material->clone (new_material_name);
                            
            Pass* pass = new_material->getTechnique(0)->getPass(0);
            Ogre::TextureUnitState* texture = pass->createTextureUnitState();
            texture->setCubicTextureName (&file_name, true);
            texture->setTextureAddressingMode (TextureUnitState::TAM_CLAMP);
            texture->setColourOperationEx (Ogre::LBX_ADD, Ogre::LBS_TEXTURE, Ogre::LBS_CURRENT);
            texture->setColourOpMultipassFallback (Ogre::SBF_ONE, Ogre::SBF_ONE);
            texture->setEnvironmentMap (true, Ogre::TextureUnitState::ENV_NORMAL);
        }

        subentity->setMaterial (new_material);
    }
}

/*
    remove the rim lighting effect from an entity.
*/
void unhighlight (Ogre::Entity* entity)
{
    unsigned short count = entity->getNumSubEntities();

    for (unsigned short i = 0; i < count; ++i)
    {
        Ogre::SubEntity* subentity = entity->getSubEntity (i);
        Ogre::SubMesh* submesh = subentity->getSubMesh();

        const Ogre::String& old_material_name = submesh->getMaterialName();
        const Ogre::String& new_material_name = subentity->getMaterialName();

        // if the entity is already using the original material then we're done. 
        if (0 == stricmp (old_material_name.c_str(), new_material_name.c_str()))
            continue;
       
        // otherwise restore the original material name.
        subentity->setMaterialName (old_material_name);

    }
}

Download of file rim.dds:
http://www.ogre3d.org/forums/download/file.php?id=2022

The code was published here:
http://www.ogre3d.org/forums/viewtopic.php?p=368918#p368918

Similar version:
http://www.ogre3d.org/forums/viewtopic.php?f=8&t=59079

For questions and feedback, please use this forum topic:
http://www.ogre3d.org/forums/viewtopic.php?f=8&t=59079