[Gabi]

I just managed to edit a mesh using Blender - http://www.blender.org/ - too. it can easily import/export an obj file. The best part is that you can add/move vertices and faces with it.
Those are the settings needed when exporting into obj format from Blender:

Blender manual : http://wiki.blender.org/index.php/Doc:2.6/Manual

Short tutorial for Blender:

Code:

A simple way to create a new vertex is to click Ctrl-LeftMouseButton in Edit mode. Of course, as a computer screen is two-dimensional, Blender can’t determine all three vertex coordinates from a single mouse click, so the new vertex is placed at the depth of the 3D cursor.

Code:

To create a face, select three or four suitable vertices and press F.