WowAce

DoubleClickForTheWin (http://www.wowace.com/addons/doubleclickforthewin/) Changelog:

    v6:
Proper changelog.
Make auction window list items double-clickable. Left button for bid, right button for buyout or cancel auction, depending on which tab you're in. Double-click again to confirm popup.
    v5:
Cleaned up a bit, more comments and making sure tradeskill stuff works properly
Make tradeskill window list items double-clickable for quick crafting
    v4:
Better handling of repeatables. Completed quests should be preferred now.
Prefer gossip, if there's only unfinished quests and gossip available.
Also prefer non-hearthstone gossip if available.
    v3:
Tweak behavior a bit. Quest item reward buttons no longer accept double-left-clicks, so you won't accidentally select the wrong rewards anymore.
Right-click still works on them for going back.
    v2:
Improve handling of repeatable quests. It will now try to find the first completed quest before considering dailies/repeatables.
    v1:
New addon, yay!