I am pulling my hair out with trying to get tfIgnore to work in Visual Studio 2013.
I followed the instructions here: bottom of this artic
In pending changes, right click the root package folder -> click undo. You should see your changes move to the "Detected changes" dialog box, under excluded changes (the window where you can promote files into source control).
Now, open up .tfignore and simply add packages. You should see that now, when you open detected changes, your packages aren't displayed.