Cacophonic Guard on the
Blasting Chime is one of the best damage guard effects in heroics.
You can also find it in Epics on the
Broken Music Box as hidden effect.
For low levels consider wearing
Rock Boots.
Some other good guard effects are Trap The Soul Guard (Instakill, Will save), Greater Disruption Guard (Undead Instakill, no save) and Enervation Guard (1d4 Level Drain, no save) from Greensteel items.
Radiance Guard (light damage + Blindness) helps you stay alive and Concordant Opposition restores HP and/or SP.
You can also find some guard effects on Tier 2 and 3
Dragontouched Armor runes in heroics.
Aside from
Golem's Heart you can also slot a
Sapphire of Crushing Wave Guard in a blue slot.
A nice Epic guard effect is Spike Guard on the
Battlerager's Harness.
A fine defensive shield with Healer's Bounty and Improved Demonic Shield:
Epic Shield of Tireless Aid
You can find Riposte XII on upgraded TOEE caster weapons.
Draconic Reinvigoration on Thunderforged Weapons has a chance to restore Action Boosts/Turn Undead/Smite Evil etc. on damage or spell damage