To recommend links is quite tricky given there is an awesome like site for all things Terragen just here...
www.terrasource.net

So stotty will simply recommend a few just to get you started. The list of people here is not limited, there are many more around whom stotty can recommend and will add more when time permits. If you think you should be on the list, or feel stotty may have missed an important link off, please let him know.

Terragen

• The Terragen Homepage (Check out the resources link there too)

Tutorial Sites

• An easy to use guide to Terragen by Carol Brooksbank Terragen Tutorial

Community Sites

• A deviantART Terragen site dedicated to submitting Tutorials and snippets of news Terragen
• A deviantART site holding themed monthly challenges Terracult
• Community Site: Ashundar Terragen Community
• Community Site: Terradreams

For inspiration, check these people out...

• Terragen Artist: Ensar Yanar
• Terragen Artist: Martin Brunker
• Terragen Artist: Luc Bianco
• Terragen Artsit: ISSE
• Terragen Artist: John Warren
• Terragen Artist: Merlin-tbd (Alan)
• Terragen Artist: Tero Tanninen (Duris)

.. more to be added soon.