Here are a couple magic rings inspired by the world of comic books (and their modern simulacra).
Rings of Elemental Earth
This pair of rings is carved from citrines and are worth 1,000 gp as jewelry. If worn one on each hand and slammed together while chanting "Res orbis operor vestri res", the wearer becomes an 8 HD earth elemental for 10 minutes. This can be done but once per day.
The ruby ring is made of admantine and set with a highly-polished ruby lens. It was forged to be a weapon against evil and can only be used by benevolent creatures. The ring must be re-charged once every 24 hours at the altar of a benevolent deity. When fully charged, the ring allows the caster to produce several spell-like effects by succeeding at a wisdom check, for use of the ring requires an act of supreme will. The wisdom check must be made every round in combat or every ten minutes outside of combat to maintain willpower. Multiple effects can be manifested simultaneously, but the required wisdom checks are made at a -2 penalty for every effect beyond the first. The ring can duplicate the following spells: crushing hand, fly, forcecage, forceful hand, grasping hand, interposing hand, magic missile (1 missile), shadow conjuration, shield and wall of force. All spell effects manifest as a ruby-colored construct of pure force. If the bearer of the ring is killed, the ring teleports to the nearest person worthy of wielding it.