ase-gui is the most handy model editor I've used to setup my VASP calculations.
It supports VASP POSCAR/CONTCAR files perfectly and a variety of other formats. The editting features (moving/rotating) are handy for adjusting surface adsorption structues.
Yet, it's a little tricky to get a nice ase-gui on windows mechaines.
- Old versions require pyGTK which is hardly available for windows, I remember attempting with miniconda and official build http://www.pygtk.org/downloads.html, but the process is tedious.
- Newer versions use tk, however the interface is ugly and some functions are not available (Ctrl+R for rotation, and zooming is buggy right now).
- VASP configuration files don't have extentions, meaning it's hard to associate them using the windows options