If you check out the link I posted previously (http://godwars2.blogspot.com/2011/07/customising-icons.html) you should easily be able to find enough icons to cover all the spells - then it's just a matter of deciding which ones to use, and what sort of colour scheme you want.
For example, I tried picking a few and colouring them blue for positive spells and red for negative spells (very quickly using Photoshop):
(http://www.godwars2.org/images/other/icons_4d.png)
If you download the latest version (http://www.godwars2.org/download/mushclient/4D_GUI.zip) of the plugin, you should see them like this:
(http://www.godwars2.org/images/other/mushclient_4d_4_small.png) (http://www.godwars2.org/images/other/mushclient_4d_4.png)
(click the image to enlarge)
However the plugin can currently only handle 30 icons (on my screen at least). If there are more than that it may be worth changing the layout - perhaps displaying them under the map, or making the avatar wider so that you can fit 3 or 4 icons per line.
That's really a personal preference thing though, now that the snippet is installed and working you can create any sort of layout you like (and that comment is directed at everyone, there's no reason why players couldn't design their own interfaces).