I like to design Magical Items that have powers that vary based on your alignment, and or class. So for instance:

QuoteMace of Justice

This Mace appears to be completely normal, except for an ornate stone set into handle.

Effects:

In the hands of a Fighter, regardless of Alignment this mace acts as a +1 Weapon, dealing an additional 1D4 damage upon a successful strike.

Alignment based effects:

Good: This Mace allows the use to cast Magic Circle of Protection from Evil, at CL 5 1xday
Neutral:This Mace allows the use to cast Magic Circle of Protection from Chaos, at CL 5 1xday
Evil:This Mace allows the use to cast Magic Circle of Protection from Good, at CL 5 1xday

What do you think of items like this? Have you used them? Would you?

Here's the only thing I don't get:  Who makes this item?

I mean, I can totally understand the purposes of items that gain powers if you're one alignment, and zap the hell out of you if you're another, and I can understand the point of just making a magic item, but why would anyone create an item that varies it's effects like that?

Maybe it was made with a generic or religion specific spell, (maybe from a god of neutrality) "Protection from Alignment" spell that adjusts its protection to the opposite alignment of its wielder, or maybe the casters intent was to create a "Protection from Evil weapon", but the caster botched something and wound up with a useful rather than cursed item. It might even be considered a cursed item if the religion is very strict in its interpretation of its gods alignment, and any follower would be under edict to destroy it and its wielder.

Maybe it was made by a good priest ("Mace of Justice" has good implications to me), some sort of Lawgiver who, in his pursuit of perfect adherence to the law, lost sight of the point of justice and became evil.

The Mace fell with him, becoming a  tool of evil - but if taken up by someone of good alignment, it becomes redeemed.

Yeah, I could see using that in a campaign.

ETA: In fact, right after I posted this I realized I could make this item the focus of a campaign/mega-adventure.

A long time ago, in a land far far away, three great heroes came together to defeat the demon Kurg'Athon.  Now the demon is rising, and the only thing that can rebind his prison is the combined power of the three weapons of the heroes.  Heinrich's Sword of Truth, Mandrakican's Staff of Knowledge, and Kaldor's Mace of Justice.

Meanwhile, the immortal and therefore evil warlord/dark priest Merciless Kar, who centuries ago seized the Southern Lands and now rules them with an iron fist, has sent agents out across the land in search of the weapons.  

The Sword was lost in the place where Heinrich fell: the Tomb of Terrors. The Staff is buried with the wizard in his impenetrable crypt.  But no-one knows where Kaldor and the Mace disappeared to.  The players must collect all three weapons of power and bind Kurg'Athon once more.

Only after they have found the Sword and the Staff will they learn the truth about Kaldor, now Kar, and his fall into madness and tyranny...