I am curious to know what addons you have and why you think it is good.
MetaMap - Just because of joanas leveling guide needs it but its still very nice. Some might prefer atlas however.
http://wow-en.curse-gaming.com/downloads/details/1978/
X-perl unit frames - hands down one of the best interface addons. Very useful in raids and such. Its possibly a "must have".
http://wowui.incgamers.com/ui.php?id=2855
MobMap - Quickly find mobs... perfect for completing quests quickly.
XBar - I find this quite nice... it helps me organize the buttons and such.
AuctionFilterPlus - I havent tried any other auction mod because this has proved to be very helpful and dont really need anything else.
Please shair your recomendations.