As requested by +Joel Priddy and inspired by +Courtney Campbell's On a Magical Shield, here are some more magic shields.
Magnetus
This iron shield has a protrusion with a coiled wire around it. When activated by pressing a button on the handle, it creates a humming sound. Any attack with a metal weapon that misses to hit by one or two points results in the weapon clinging to the shield, requiring a complete action and successful strength check to free the weapon. Any attack on a fighter that is holding onto a weapon currently clinging to Magnetus receives a +1 to hit.
Ith-Narmant's Shadowshield Glove
When not in use, it looks like a pitch-black glove that does not reflect any light. When activated by clenching one's empty hand, a disk of magic shadow forms instantly at the back of the hand, protecting the wearer like a normal shield.
The shadowshield provides an additional +2 AC against attacks with any fire or light-based weapons as well as a +2 bonus on saving throws versus any fire or light-based magic or effect. The saving throw bonus also applies while the glove is just worn without the shield being active.
This glove is a given as a reward for extraordinary services to priests and champions of Ith-Narmant, the master of shadows, chill and solanaceae. Prolonged use by others might result in the visit of Ith-Narmant's agents.
Displacer Shield
A round shield covered in the dark blue pelt of a magical beast. The wielder of the shield appears to be one foot away from their actual location. In addition to the AC bonus of a normal shield, the displacement effect gives any attacker a -1 on their attack rolls.
Any other action that involves the need to know the location of the shield's wielder, like a cleric's healing touch or chucking a weapon to the displaced fighter, also either requires a successful perception roll at -1 or incurs a -1 on the roll for the action, as applicable.
Double Displacer Shield
As displacer shield, but combining pelts from two magical beasts, displacing the wielder two feet and resulting in -2 on all applicable rolls.
Paineater
Not a shield per se, this symbiotic magical bug can be implanted in the back of one's hand or forearm. In its dormant state, it looks like a big grey wart. When the host loses hit points, the wart quickly grows into a buckler sized shell and sprouts up to 4 chitinous tentacles that actively deflect further attacks.
The AC bonus is equal to the lost hit points, up to a maximum of +4. Each attack that does not hit the host reduces this AC bonus by 1. Further hit point loss increases it again (up to +4). Any healing of hit points also reduces the bonus AC.
The arm hosting a paineater bug cannot be used to wield a weapon or sword. Extracting the bug is only possible by cutting it out of the flesh, resulting in 4 damage.