GIMP :: Creating Great Looking Game Textures

How to make textures look great around the edges and blend nicely with the background.

Here's a sample of my problem, here's how the texture starts to look:

Here's it is rendered against a smoky light colored backdrop:

Here's how I want it to look, the edges are so nice!:

Here's the above ball zoomed in:

I can add shading in the .png file but then I can't render it properly as the shaded geometry messes up when I created the transparent background.