WowAce

Adds tooltip for debuffs (and other things? you found out: no).

Tooltip of socials button will now show which friends are online

Show extra information about Jewels and Enchants in tooltips.

Shift-clicking on a user name in chat shows a tooltip with their whois information.

Mob respawn timers

Shows what stat was reforged in item tooltips.

Allows the user to customize the the tooltip with lua-scripts

LCDs for WoW

Adds information about the items tokens can purchase and vendor location to tooltip

Enables RatingBuster to calculate selected buff effects even if you don't really have them

Sneakily inspect how much gold your mouseover target has made so far.

Never forget which one in that 5-mob pull casts what spell again.

Keeps track of Gimps and warns you if you end up grouping with them.

Addon to add more information on a Tooltip to the GuildRoster

Shows the Guild Achievements Points and Members in the tooltip

Calculates the relative value of attributes towards physical dps.

Item link modification

Ratings

LibQTipClick-1.0

Adds tier set number and difficulty indicators to tier item tooltips.