Zanzil's Concentration is a set of rings obtained from Zul'Gurub, Zanzil's Seal is dropped by the infamous "raptor-boss", Bloodlord Mandokir. The ring is likely to last a small moment during your leveling process in the Outlands, if you have obtained it somehow... and now to the other ring.

Zanzil's Band is dropped by the "snake-boss", often said to be the easiest encounter in Zul'Gurub - High Priest Venoxis. This ring has a combination of intellect, hit rating and mana regeneration, which makes it a pretty neat ring to help you preserve your mana (intellect turns directly to mana, hit rating will help your spells hit the target, making it more mana-efficient and the mana regen is simply useful because of the fact that it restores mana)

Upgrades from the Outlands-territory

Band of Renewal - obtained from Reinforced Fel Iron Chest which is located in Hellfire Ramparts.
Witching Band - obtained from Reinforced Fel Iron Chest which is located in Hellfire Ramparts.
Sage's Band - obtained through reputation, alliance.
Farseer's Band - obtained through reputation, horde.
Golden Draenite Ring - a cheap ring often found from the auction houses, crafted by jewelcrafters.
Adept's Band - an easy quest for the alliance.

The whole bunch of them in one link.

Hope you found this post helpful, I sacrificed a moment of my precious "life" writing it, all the research is done by me, as wowwiki didn't offer me his helping hand. Oh, and by the way, here is the wowwiki-article of this item-set.