General rule of thumb (this is not an exacting way to really tell:
If it damages you, its afflictive.
If its a maledictive, well, its maledictive (duh). The list of shaman spells are a good guide here.
Most others are mental.
Here's the thing that got me though. The definition of a malediction is like a curse (not the actual spell curse) or execration. So, spells like plague, a shaman's blindness, dysentry, hex....all maledictions.
But take blindness (not a flamestrike style blindness, or dirt kick..the actual affect 'blindness'). When cast by a shaman, it is a malediction. But when a BMG casts flashfire, even though the resulting affect is the same blindness affect as a shaman's, it is not -technically- a malediction because the blindness is a result of bright light and not a curse/execration. Would then, flashfire be saved against afflictive (I'm not asking the question, just raising a point to think about and to experiment with), even though the blindness type is the same as a shaman's malediction, or would it still be recognised as maledictive? Has a good chance of being either of the two.
Dey
EDIT: Umm..just realised I basically said exactly what Aulian asked except it took me three times as many words. Great going, Dey. 