I've been working some times on a particle editor, i've called it Ogre Particle Lab, it uses QT for the graphical user interface.
Features:
. All Ogre3D(v 1.6) default particle features availables: attributes, emitters and affectors.
. Reload resources, materials/textures and particle scripts at runtime.
. Pause/resume particles.
. Friendly camera.
EDIT>>
. Camera tab(change background color, texture or FOV).
. Light tab(usefull for shader based particle effects).
. Stereoscopic view parallel, crosseye or Anaglyph (using F1, F2, F3).
EDIT<<
Most of the time parameters are linked to 2 widgets, for example a knob(or slider) and a text input, so if the
first one is too limited in range or if the setup is not appropriate you can still enter the numeric value directly.
I tried to add tooltips almost everywhere(based on the Ogre Manual).
Here are some screens:






I've also uploaded a youtube video(in frenglish): (EDIT: old beta version)
You can download it there.
Hope you like it,
Feedback welcome.