[Hengist]

I am looking for an addon which can show me how much time is left on my and only my Rend.

[Rishkkin]

I use Satrina Buff Frame for that.

Satrina Buff Frames 3 : WoWInterface Downloads : Buff/Debuff/Spell Mods

[Helgi]

Rishkkin has what I use for rend.

Also use Power Auras to put a huge logo in the center of my screen with Rend expires since my mind is frequently off on other things in the middle of combat instead of keeping track of my rend.

[Niian]

NeedToKnow

[Naifon]

Best addon for this is Debuff Filter:
Debuff Filter - Addons - Curse

Can setup so you only see your Rend and everyones rend/tc/demo etc. Use it togeter with Power Auras to place a big flashing arrow with a sound when you dont have rend up =win.