Is there an addon for todo management? Like something that hooks into the text editor, or maybe the node editor?

I'd like an addon that allows me to keep track of things I'd like to do (or have done) on a model.
You can use Generic Note Add-on which allows to create some kind of sticky note in the Compositor. In this case I'd suggest re-using a text file from the Text Editor:





In addition there is a nice Comment Node Add-on by @CoDEmanX, which allows creating a list:





Since Blender 2.74, you can use the built-in Frame Node to display text blocks in the Node Editor: 



Further information: Is there a way to make comments in the node editor?