Ha
I use Lee ND Grad Filters, fantastic reputation. I also use a B&W (brand, not style), ND1000, which is a 10 stop.
The Lee Filters, you can get soft or hard edged, which will determine how extreme the gradient is. Basically use them to hold back brighter areas of an image (Normally the sky)...
With the filter system I got, you need...
Lee Wide Angle Adapter Ring (depending on lens)
Lee Universal Hood (Lovely!)
Lee Soft ND Filter Pack (.3, .6 and .9)
I paid about £250 to £280 ish.
The B&W 10 stop blocks so much light, that you can get really REALLY long exposures throughout the day. I think it an absolutely stonking bit of kit, your shots can adopt an entirely new look. Great for STATIC landscapes (Moving clouds is OK), and Swirly seascapes.... I paid £80 or so.
There are other filters, but not that I use. I have a circular polariser, but dunno how best to use, so it stays in bag.
Fancy having a stab? Landscape photography is absolutely relaxing, fun and it opens your eyes big time. I love it.
Gary.