Whilst my five stars and above title suggests that this Hoya 77mm pro digital polariser is the best, I will admit that I had hoped to get the Sigma version that in its 82mm guise, is absolutely superbly engineered. I use that (& review) on my Sigma 24-70mm f2.8 HSM, the results of which are stunning.
One of my most used lenses, the pro Nikkor 17-35mm f2.8 that I use on my full-frame Nikon D700, is about the widest angle of view available in a lens that has front mounted filters. 104 degrees diagonally - that is a lot of blue sky and a deeply saturated colour landscape, especially a seascape with brightly coloured boats, for example can be quite simply transformed into a tropical paradise - from an average sunny day in England.
It's a slim filter - which means minimal vignetting in the corners at 17mm (though not as slim as that Sigma) and is sturdily made. It's used almost all the time, when the conditions suit.
I've used polarisers most of my photographic career and would always sing their praises. However, they can be frighteningly expensive, almost as much as some new lenses. Very cheap ones (I review a Hama one, for example) literally aren't up to the job and cause frustration when they fall apart after only a few photographic excursions.
Do remember this - when tilting the camera from a vertical to a horizontal shot, the angle is changed and so is the polarisation. Though a bore, you do have to rotate the filter to get the best effect for each photo and deep lenshoods on telezooms can be a bit of a nightmare - but I always take the trouble. Look out also for zoom lenses that boast 'a non rotating front element', usually they've got 'internal focussing, or IF', so watch out for that in a lens' description - that way, once you've got the right effect and then change composition by zooming, you won't have to reset the polariser.