My Tutorials & Articles:

• Tone Mapper Tutorial - Method for reducing global contrast and increasing local contrast
• Contrast Adjustments - An interactive page with a comparison of 5 different contrast adjustments.
  

Links of Interest:

• Gimp Guru - Great site with Gimp tutorials and info
  
• Luminous Landscape - Not Gimp specific, but lots of good digital photography resources
• DP Review - THE authoritative site for information and comparisons on digital cameras
• Bob Atkins photo site - Great site with articles on digital photography (like this discussion of sensor size and this discussion of aperture and sharpness) 
• Incident Metering for Digital - Good discussion of why you might consider a handheld incident meter instead of relying on your in-camera matrix metering.