Addon Spotlight takes a look at the little bits of Lua and XML that make our interfaces special. From bar mods to unit frames and beyond, if it goes in your Addons folder, we'll cover it here.
Daily Quest Viewer is my favorite kind of addon: it solves one problem well. It tells you what today's daily quests are, enabling you to stop pestering your guild (or the trade channel) for information. My guild has developed a policy of putting the daily dungeon and daily heroic in the message of the day, but that only works if an officer has managed to check the dailies and update the message.