WowAce

Point to quest POIs on your minimap

Easily mail friends, guild members, alts and others

Adds party/raid role icons in useful places

FuBar_AmmoFu

Inspects all members of raid and saves in database, as well as lists people's dkp values

Adds the toon name to the alert that your RealID friend has come online.

NRT_EPGP

Buffalo

Plays sound when a ready check, LFG queue, battleground queue, or world battleground queue pops even if you have sounds turne...

Provide plenty of links

Libra

Gives a score for your kit allowing easy comparison with others, also colour codes kit based on appropriateness for your level.

A data broker display, that shows one block per plugin.

Pop a chatframe warning about guild battle standard when boss health reaches 30%

aUF_RangeCheck

Database of Diminishing return categories and general data

A tool to appraise, estimate, or judge your equipment against the equipment of others.

Heal and decurse by clicking on customizable raid/party unit frames

Add-on that shows which mounts can be farmed this week

SupplyAndDemand