Here's a random topic: I've never really liked the way RPGs handle wishes. To me, a wish is not a superpowerful spell that alters reality; it's simply one person expressing a desire and another fulfilling it, through any means available. Anyone could grant a wish, but for every person or being, some wishes are beyond their ability to grant. Some wishes may require a lot of work, for some wish-granters. And, for supernatural beings, it might be possible to grant extreme wishes very quickly.
This, to me, is the key to limiting the power of a magic ring of three wishes or the like. You can't wish for more wishes because a wish is not a thing, it's an action (speaking your desire aloud.) Anyone, even we here in non-magical reality, can already make thousands of wishes a day; they just won't (usually) be granted. Similarly, since some being must fulfill the wish, the easiest way to "twist" a wish in the traditional manner is to decide what the being's limitations are and what the being could do to grant the wish or at least come close. If you wish for a magic item, it has to exist, or the being has to make it (or find someone who can.) If the item already exists, taking the item from its current owner or bringing the wish-maker to the item's location fulfills the wish, but might cause additional problems. If the item doesn't exist, making it may take some time and may require a series of steps, each of which may have consequences.
What stands out as interesting about wishes in folk-tales and legends is not the process of granting the wish, but the agreement to grant wishes. Beings with extreme wish-granting abilities -- djinn and efreet, demons, fairies, the Devil himself -- seem to have extreme magical powers, but they rarely if ever are shown using such powers for themselves. What I would propose is that the Wish spell (if it exists) or wish ability inherent in such beings is actually a variant of a Geas or Quest spell which sets up a binding agreement between a wish-granter and a wish-maker. A bound wish-granter gains the ability to cast an unlimited number of spells, including spells known to exist but unknown to the wish-granter, but only within the context of the agreement.
This usually means that the wish-granter can't cast a spell on the wish-maker at all except to grant a wish. Once the agreement has been fulfilled, though, if there was no stipulation as to what would happen after the granting of the last wish, the wish-granter may be free to take vengeance, if desired. I'd suggest playing out the negotiation of the agreement, taking into account the basic feelings of the wish-granter towards the person demanding wishes. If a player suspects that the djinn begging for release from the bottle is the slightest bit hostile, it would be wise to add some kind of protection clause.
Some interesting variants would be lesser beings, including elemental lords or a genius loci, which can only grant wishes through a particular medium. For example, a djinn might offer "three wishes that can be granted with wind and air". This would remove the possibility of certain spells (Earthquake) and would require other spells to be reskinned as due to magical winds, clouds, and gasses, possibly even restricted according to this description.
The benefit of playing wishes this way is that it's not just a quick "wham bam thank you ma'am" interaction with the wish-granter, and things don't just appear as the wish is spoken. There's more of a back-and-forth, with a less-hostile wish-granter asking what the wish-maker means, or telling the wish-maker that it will take some time to grant the wish.
And as for reality-changing effects... well, I have some ideas on that. But that's for later.