World of Warcraft Wrath of the Lich King
You will find it handy for your in-game experience.
This addon shows user comments from wowhead.com to help questing. It is a modified version of the original qComment addon (credits to ostap).
PetShop will track every Companion your toons knows and add lines to the GameTooltip to show you which toons currently have that Companion and which toons are missing it.
AutoProfit adds a small icon to merchant frames that allows you to sell every gray item in your inventory to the vendor instantly. You can also configure it to sell certain white items too.
EpicMusicPlayer is a ingame mp3/ogg music player with multipe playlist support a fubar/titan panel plugin and a fancy little 3d model.
SpamSentry by Anea stops goldspam messages from showing. You can use a one-click report system to create a GM-ticket for the caught spammers. Both spammers and bots can be reported manually as well.