Could any1 give me a list of useful open source programs compatible with blender? There seems to be so many I don’t know which to get 
open source programs that do what?
or are compatible how?
[if you aren’t more specific all open source programs can be listed]
Yep that’s the problem, and wait 4 it
… I DONT KNOW
On an impulse I just got Gimp and Terragen and I don’t even know what they do yet!!!
The Gimp is probably all you need for now.
Most importantly - learn Blender (and 3d modeling generally). That process will let you know what other tools you “need.” 
Once you get into animating, you can get into things like video editing and compositing (and maybe even movement matching).
But, a journey of a thousand miles begins with a single step.
Yah, “compatible” is a little vague. ‘Needed for creating good blender scenes?’ might help to focus a little.
A good bitmap editor will almost certainly be necessary and I find a good vector map program for adding things like signatures and maybe borders helps a lot too since the text is much easier to manipulate (although GIMP can do that too). Inkscape is the open source vector map app of the moment.