Time to get a neutral density filter?

I've never had one but think maybe it's time to have one in my kit.
I'm thinking of a three stop 82mm fixed type. I have been happy with the B+W filters I own, but as often as I expect to use a ND filter not sure I want to spend that much.
Part of my problem may be GAS as I haven't bought any photo gear in over a year.

So, is three stops about right, and what brands should I consider?

What application? I think you'd benefit from having a range of choices no matter what the subject is.

As an example, I recently experimented with ND filters, and chose to limit my budget until I had a better understanding. I chose the ICE brand filters through amazon with pleasing results. I use a 10-stop for scenic work with a tripod, and a 4-stop for portraits. I plan to expand the range of stops for portraits (2, 3 and maybe 6). I look forward to hearing from more experienced users.

Landscape/waterfall are the most likely uses I think.

One thought is to look at your current landscape/waterfall photos and note the shutter speeds used. Calculate what 3 stops would do to the shutter speed and then try and locate photos on Flickr with close to those shutter speeds and determine if they have the look you're going for.