I do like the first one. Do you use a polarizer and/or ND grad filters?
I think 2 and 3 could do with a bit of help on the exposure - to avoid that blown out sky and the reflections on the water, but retain the detail in the darker greenery. Nice shots!
Things are looking better. As said, you need to work out how to darken the sky. As it happens, my Cokin polariser & filter kit is up for sale in the for sale section - grab yourself a bargain
Will the filters fit? Depends on the filter thread diameter of your lens. On the front of the lens you should see a little circle with a line through it followed by a number of mm. This is the lens filter thread diameter.
The Cokin filters use adapter rings which screw into the filter thread. You can then use the filters on lots of different size lenses. The smallest adapter ring in my kit is 52mm.
Tobers