Vranx

MyThreat Brimm

MyThreat is a simple compact frame containing three simple values: Your threat percentage relative to the current target's threat, Your threat difference relative to the current target's threat, Estimated time to surpass current target's threat assuming constant TPS.
WoWInterface

lolThreat Lolzen

Puts a Simple text on your screen, giving information about your current threat, of your target.
WoWInterface

NoThreat Rakzul

Extremely minimal addon that displays a percentage display showing your current threat compared to the tank (target's target). Shows a value between 0% up to 130% so you can quickly see when you'll pull aggro based on melee/ranged distance (above 110% in melee range, above 130% for ranged). Can also (optionally) display the name of the current tank.
Configuration is done by editing the lua file and should be fairly straight forward, there are no in-game slash commands. When configuring, unlock the display by editing the lua file, change the X and Y coordinates and reload your UI. When the display is where you want it, change the display back to locked and reload. Threat display will only show up if you're in a raid, a group or if you have a pet out.
Config: Lua
WoWInterface, Curse

Omen Threat Meter Xinhuan, Antiarc, Nevcairiel, anmoch

Omen is a threat meter. Basically, enemies in WoW decide who to attack by deciding who is the most threatening based on the abilities you use. What Omen attempts to do is provide reasonably accurate estimates of your group's relative threat level on individual enemies, so that you can see when you're in danger of pulling aggro (or, if you're next on the snack list if your tank bites it). This info is usually only critical in raids, where only tanks can survive aggro, but it's useful for any multi-player situation.
Curse, WoWInterface

sThreatMeter2 Shantalya

Simple threat meter. German localization but it works fine on English clients. Must edit the Lua code to move it.
WoWInterface
Vranx Note: The screenshot shows a modified sThreatMeter using the smoothV2 texture.

Simple Threat Meter Amethyst

Simple Threat Meter was designed out of a desire to be able to see what my threat level was, simply and without having to visually locate a mod and study it. Omen does such a great job that I haven't seen many other threat meters developed, but with the complexity of some fights, I wanted something that keeps me aware of my current threat level, but allows me to focus on the fight at hand. So, Simple Threat Meter was born.
WoWInterface

TidyThreat danltiger

A raid-worthy threat monitor, which is simple enough for a new player to understand, yet powerful enough for a progression raider. The status bar shows your threat compared to the maximum threat for the rest of your group. In other words, if you are the top threat holder, it will also show how much your threat exceeds the next highest. For additional data, players can enable the Detail Window, which will display real threat numbers. Tidy Threat also adds threat data to your tooltips, allowing you to read AoE threat via mousing over the unit.
WoWInterface