Gimp for Textures?

I use the Gimp for creating the textures that I use in Blender. My problem is I don’t know how to create a good pattern for a repeating texture.

I have seen some paint programs where you can activate a setting, and then be able to paint all the way to one edge and have your cursor appear on the other side of the canvas. This allows you to create a pattern easily.

Does the Gimp have a feature like this one?

nope

but you’d do it this way in the gimp:
paint the middle
shift+control+o [offset filter], choose x/2, y/2 and confirm
paint in the middle
shift+control+o [offset filter], this time choose x/2, y/2, but then go back and set X to 0
repeat

the other thing you can do is filters>map>make seamless

try it out if you havent already

That never really works properly; you still get seams when you tile the texture

Try texture ops plugin.