Cooldown Notification
Flash the icon of the ability in the middle of your screen whenever it becomes usable again.
This would, of course, be optional and disabled on default.
Source: http://wow.curse.com/downloads/wow-a...downpulse.aspx

Buffs & Debuffs
Show timer on buffs and debuffs, aswell as categorize them.
This is not about respawns of Blue or Red buff.

I like this. I used an addon playing WoW that did just this same thing.

It would be annoying as ****, especially when spamming Karthus q or something like that

If you don't like it, don't enable it. For me, and probably a lot of other players who might've used addons like this in other MMO's or MOBA's, will surely find such a feature very helpful.

E.g. http://forums.heroesofnewerth.com/sh...oldown%20Pulse