BuffUptime

This WotLK-only mod will track what buffs are up every time you attack. It's primarily an analysis tool for tracking the frequency/coverage of proc buffs like Enrage and Executioner.

To summon the window, you can set a key binding or use slash commands:
/but to toggle the window
/but on to turn logging on
/but off to turn logging off
/but reset to reset logging

In the window, you can turn logging on or off, or reset with buttons in the titlebar.

It doesn't track buffs during misses or resists (the buff contributed nothing then), nor does it track DoT ticks as a hit.