Natur enemy castbar started as a pure PvP timer but has grown into something that really can fill up your screen.
http://wow-en.curse-gaming.com/downloads/details/2786/
I am not sure what you are looking for; if it is to have 40 timers of debuffs, or even if the mod is configuarble in to that purpose. But It's one that I can think of which has debuff timers.