I never evolve my Pikachu. Never. Other than the fact that Raichu is a hideous piece of garbage, I always will give my Pikachu a Light Ball. In other words, I'm sacrificing an item slot, but I end up getting a cute Pokemon in return with a stronger Attack and Special Attack stat than its evolution.
I also played to the end of HGSS with a Growlithe, and I mean the end. I was planning on evolving it, but I never found a Fire Stone during my playthrough. I had a level 70 something Growlithe when I went up against Red. After all that we went through, I decided to just never evolve him.