Ring of the Cobra
When this ring is worn, the wearer’s eyes transform to those of a snake, his tongue forks, lengthens, and flicks about, and he grows fangs. The wearer’s sight, hearing, and smell senses are dramatically heightened, giving a +2 ‘to hit’ in combat, providing a -1 bonus to armor class, and imparting additional benefits as appropriate.
Also, the wearer can attempt to bite an opponent, and a successful hit delivers 1d6 of damage. Bite victims must save vs. poison or become paralyzed in 1d6 rounds for 1d6 turns. Those that fail their saving throws by more than 4 will die at the end of the paralyzation.
The ring of the cobra, however, is not all beneficial. Once put on, the wearer must make a successful save vs. magic to remove it. This can be attempted each round and takes no extra time, failure simply indicating that the ring cannot be removed that round. Additionally, while wearing the ring, the owner is subject to all effects which affect snakes (example: snake charm); if able to remove the ring, this vulnerability vanishes immediately. Finally, the wearer suffers a -4 penalty to charisma while wearing the ring (for most creatures) due to his appearance. (Note: These disadvantages may not be immediately apparent to the ring’s owner.)
I prefer most magical items to have some downside. TANSTAAFL.