Because digital cameras have so many automatic settings such as white balance you don't really need to use as many filters with them. There are a few that can be helpful in digital photography and these are ultraviolet or skylight filters, polarizing filters and neutral density filters. These filters are used because the effects they give can not be duplicated electronically by a digital camera.
You don't need color conversion filters since you get its effect by adjusting your camera's white balance. Another advantage of the adjustable white balance is that you don't lose the f stop that these filters absorb in film cameras. You can also use filtering effects in most imaging software programs that come with your digital camera.