Having recently installed Proeder's File Attachment mod, I noticed it did not have a progress bar indicator letting users know that their file was being uploaded.
This addon will give you a progress bar indicator when a member uploads a file. Note that this progress bar is simply an animation and does not actually measure the upload progress. It does however give your members the peace of mind that their file is uploading rather than staring at a static screen.
You can get it here.