Addon

[BenBu]

Is there any addon that shows me when I have reached 5 stacks of weapon of maelstorm? I'd like to know when my I can cast instant heals

[Shadygnome]

Explore wow.curse.com

Nug combo bar seems to be the default choice, but i hate the looks. Almost any combo bar addon for a rogue/druid has been updated to work for shamans too.

[RazoRez]

I use power auras classic ^^ for it :D

[Anodyne]

There are a few that show it, including some, if not most, unit frame addons, though that is hardly ideal.

My vote would also go for a Power Auras setup, since you can make any sort of visual demonstration you want with it. In my case, I have a totem graphic pop up for each stack of Maelstrom Weapon I have, and at five stacks they disappear and are replaced with a large lightning icon thingy, along with playing a little ding noise to ensure I don't miss it. Of course it can be configured any way you like, it's got plenty of customization to it.

[Neoxid]

Power Auras is awesome for that (also useful for plenty of other things)

[Extremoos]

Maelstrom maelstro, also does a sound when you reach 5 stacks

[saqibious]

Try the add on Tell Me When