So there're two main rewards upon completing this quest, apart from the exp. The first is an updated ring, which lets you access the portals you previously could not, like the one on that odd island east of the Chaos Elemental. Additionally, you can now access invisible portals. These are apparently found in 'spiritual places' (don't remember the right words), so you basically look for a place with ghosts, and start operating the ring square by square, which is an awful lot of fun.
The second reward is that shield. Apart from already having fair bonuses, you can get it blessed and add some 'Sigils' to it. These Sigil things can boost the shield's stats, and can be found around the wilderness - my guess being, inside the invisible portals.
I'm yet to explore anything, so if you've additional information, feel free to post.
Update: Viewing the Other Armour section of the in-game Smithing guide, you can see that these shields have quite lovely requirements. My guess these are in par with the Dragonfire Shield, but offering defence in a specific category (slash, stab, etc).
Viewing the Prayer guide, you can see these require some serious Prayer levels as well (likely to put off dragon bones prices up the ass again).
Edit: My guess is that the main game manual on the official website will include full info on these shields tomorrow, once the spoiler lifts off.
Update: Ladies an gentlemen, the price of the sigils is revealed: http://itemdb-rs.runescape.com/results. ... l&members=
