Budget & lens filter thread size?
You can keep things simple and just get a circular polarizing filter to remove window reflections and preserve a little sky or you can go for the slide on filter route like Cokin, Hi-tech, Lee or Singh Ray that are great for landscape with clear horizons.
http://www.singh-ray.com/grndgrads.html
If your shooting in low light a tripod is must if you don't have one already.
These 85x110mm filters fit in the Cokin P filter holder* and are manufactured from the highest quality optical grade polyester resin.
*May not fit in some newer Cokin holders - please check before purchase.
its a joy to use. great bit of kit would love to learn how to use it to its full useage but just do not have the time with uni and all. are there any good books on dslr's? for tips and tech'.
thanks bluepete, the above are for moving water. what would be best for day light buildings and landscaping i always get white sky's even what playing with the white balance?
cheers