The item causes a random spell effect to target a random target within the combat(roll to determine which target, roll a d4 for spell list(Cleric, Druid, Wizard, Psion), roll a d10 for level(1-9, 0 or 10 is cantrip) The spell acts as if cast at a random CL(d2, then a d4(the 2 determines negative or positive, the d4 adds to the hd of the target.)). If the spell has multiple effects, the DM chooses the effect. Roll to determine which spell is used(I suggest the SRD)
Mostly the same thing, but the wielder determines the level of the spell, and any optional effects.
Still the same thing, but the striker chooses.
This is somewhat complicated, but is really random. You might want to roll to determine what school of magic is used to narrow down possible spells.
The spell is treated as though cast by the target at the target. If the spell would normally not affect the target, it does.