Start with a basic $40-$60 filter from a good brand: Hoya, B+W. Avoid a slim since you will not be able to use a lens cap while it is on the lens. Some wide angle lenses will need a slim but check if your lens will really needs it. If this is the case you will get black corners. The polarizer filter is the most important and the only one I use. Check out my pictures. I get by with a couple of cheap polarizer filters from Quantray.
