[KenCo]

Digital cameras come with there own in built uv filter, so all an additional uv filter will offer is protection.....still a good idea and saves any damage to the front glass of your lens. As for makes/brands the better names are (in no particular order) B+W, Heliopan, Tiffen, Singh-Ray and Lee....These can be expensive BUT depending on what you really want and how much you want to spend, you won't go wrong with any of these. Next you have Hi-tech, coking pro and hoya pro etc these are a little cheaper (although not a lot) I bought a Lee holder with Hi-tech filters (3 nd grads & 3 nd's) for a little over £200....The cheaper you go the more likely you will get colour casts etc, although they do the job intended but at a cost. ....especially with the cheaper makes you may notice image degradation....having a quality lens and putting a cheap filter in front will compromise the image and the more filters you wish to use together the more it will effect the outcome. If you only want to have a play with filters just go for the cheaper cokin, then when you know what you really want you could invest in a good set. I'd also consider the slot in type, rather than the screw on type (depending) this way you will only need to purchase the adapter rings for your different size lenses rather than having to buy different size filters.
For landscapes it would be a good idea to get a set of nd grads these will reduce the light in the sky enabling a better exposure for foreground. Slowing shutter speeds for the milky water effect you will need a set of nd's (neutral density) and a cp will reduce reflections and or enhance the blue of the sky...I priced a Lee or Hi-tech cp a while ago and it was about a £100, think I will have to wait a little longer!
HTH.
Ken.