Hi, welcome to the forum.
You may get a better response by posting this in the beginner secton, or equipment section.
ND grads are great for landscape photography, but it is possible to bracket your shots and merge them in photoshop to get the same effect. This saves buying the filters, and using them.
Lee, Cokin, Kood, Hi-tech all make filters of varying quality and price.
I have Cokin and they're ok, but not the best.
They come in hard and soft, and in different densities.
You need to make sure you get the right size holder too.
This is the sort of thing you'll be looking at!
http://www.amazon.co.uk/Hitech-Grad-...192831&sr=8-13
http://www.wexphotographic.com/buy-l...r-kit/p1534482
http://www.wexphotographic.com/buy-c...r-kit/p1000795
Hope this helps.
Chris