Elnia at the Pink Pigtail Inn has some excellent and interesting advice for Blizzard's quest designers (or whoever they hire for the current position). As big a component as quests are in the game, they haven't been innovated on much since the game's release. Blizzard has played around a little bit with allowing us to repeat certain quests, and they've streamlined the group questing mechanic, but other than that, quests are pretty much the same: pick up a task, do it, and bring it back for a reward.
So how can it be done differently? Elnia has some great ideas: she asks for quests that span a little farther, that push players through a storyline that might even follow them all the way up to 80 (of course, there are quests like that, though they're few and far between -- and not all players have the patience to finish them). Rewards could be mixed up, too -- instead of the old gold and XP, how about some profession skill, or a tradeoff of badges based on certain quests done. Finally, Elnia suggests that every quest in the game become repeatable. Questing is paced to keep us interested in from 1-60, but we all know how the game works now -- why not let us do some of our favorite quests over more than once?
I'd suggest we go even farther -- Warhammer Online offers Public Quests that are an interesting twist on the usual "go kill boars" mechanic. I'd like to see branching quests with more than one outcome -- maybe a moral choice to make that affects the storyline of the quest you're doing. And talking real pie-in-the-sky here, I'd like to see questgivers treat you different based on the way you look or maybe what title you've got equipped. If you've got "Jenkins," they might not expect you to do much, but with "Champion of Ulduar" over your head, they should probably be groveling at your feet.