I use cooldowncount that show up on your action bars, but thats not really an alert. There are 2 mods I have seen that show up as bars.
http://wow-en.curse-gaming.com/downl...down-bars-2-0/
or
http://wow-en.curse-gaming.com/downl...wn-timer-bars/
I don't use either nor do I know they work, but they look pretty good if this is what your looking for.