While only the ones noted for conferring XP bonuses will actually increase your leveling speed, heirlooms do not have any durability which will save you money over the journey to 80, and also are usually on par with a good blue item of your current level. While once you get to the higher levels you may find things that fit the slots better, these are solid choices especially pre-60.
I would recommend the following items:
This will provide a 10% XP bonus when equipped:
Tattered Dreadmist Robe
Tattered Dreadmist Mantle
These are the PvE shoulders, if you plan to Level via PvP at all, you might consider the crit and resilience on the PvP staff instead of the int and the regen (via the spirit) on the PvE one.
Exquisite Sunderseer Mantle
Both of these shoulders will provide the 10% XP bonus when equipped, the bonus stacks with the shoulders and the ring.
Discerning Eye of the Beast
These stack and you can use two of them, so I would use them for both trinket slots.
Dignified Headmaster's Charge
This will be the best weapon for Healing.
However, for Shadow, the hit rating on the PvP staff is great. Hit rating is a very hard stat to come by prior to higher level gear.
Grand Staff of Jordan
Finally, if you can manage to win the Kalu'ak fishing derby, you can get an extra 5% XP bonus:
Dread Pirate Ring
The following enchants will work on your heirloom gear:
Enchant Chest - Major Mana
Enchant Chest - Greater Stats
Enchant Chest - Major Health
Enchant Weapon - Spellpower
Enchant Weapon - Mighty Intellect
This enchant will not work until Level 70, but it can be applied to heirloom gear:
Greater Inscription of the Gladiator