Please keep in mind that anything that improves normal defenses, such as Improved Defenses feat, will also improve your Total Defense.
That said, here is a list of stuffs that specifically works for Total Defense:
Items seems to directly enhance your defense:
- Parry Gauntlets (Level 5, Adventurer's Vault) +2 item bonus.
- Defensive Weapon (Level 2+, multiple books) +Enhancement item bonus.
- Ring of Vigilant Defense (Level 17, Adventurer's Vault) +4 item bonus.
- Sword of Kas (Epic Artifact, Open Grave) +5 item bonus.
While feats tends to give your total defense some rider effects:
- Timely Respite (Heroic, PHB2) Make a save when you total defense.
- Shifting Defense (Heroic, PHB3) Shift 1.
- Watchful Redoubt (Heroic, PHB3) +1 attack roll.
- Warding Defense (Heroic, PHB3) Shield; Adjacent allies gains +2 AC and Reflex (untyped).
- Gathering Night (Heroic, Dragon 382) Dusk Elf; Total defense make you invisible.
- Turtle's Shell (Heroic, Dragon 383) Druid; Resist 5 all when in beast form.
- Steely Defense (Paragon, Dragon 379) Two handed weapon; Melee attacker takes Strength modifier damage.
- Defense of the Inspired (Paragon, Dragon 381) Warlord; Gives total defensing ally +Charisma modifier bonus to defense.
A few Class, Paragon Paths, and Epic Destinies grant additional effects like feats:
- Knight (Heroes of the Fallen Lands)
19th Level; Grant adjacent allies +2 defenses.
- Scout (Heroes of the Forgotten Kingdoms)
19th Level; Shift 1.
- Arena Champion (Dragon 368)
Martial, 11th Level; Next attack +Cha mod/2 untyped bonus.
- Ghallanda Sanctuary Guardian (Eberron Player's Guide)
Mark of Hospitality, 16th Level; Total defending allies + 5 + Cha mod temp hp.
- Faithful Shield (Divine Power)
Paladin, 16th Level; Those who hit total defending allies gets 5 + Wis mod radiant damage.
- Twilight Tribune (Heroes of Shadow)
24th Level; Total defense make you insubstantial.
If you have can deal damage outside of standard action, such as aura, stance, minor action attacks, interrupts, conjurations, or summons with instinctive actions, and you stack them up, perhaps min-maxing Total Defense is workable, espcially if you are trying to solo.