UV filter serves no purpose for a dSLR, which has a built in filter in front of the sensor to remove UV. Many, however, subscribe to the 'UV filter helps me avoid goopy toddler fingers' school of thought, even if hoods provide better mechanical bumping insurance. Some of that is the thinking that it is 'better to clean a filter, which is replaceable, than to have to replace the front element of my lens!' Also, a UV filter protects from abrasion in blowing sand, and is also useful for a bit of salt spray protection to the front of the lens.
CPL filters help with color saturation, particularly of the sky (the portion at 90 degrees from where the sun is) as well as helping to remove reflections (glass, water surface) and can help with photographing automobiles because of the improvement to the perceived saturation of the paint because of removal of surface glare from the paint.
The wisdom is to get 'Multicoated' or 'Super Multicoated' filters, due to the increase light transmission (97% with multicoating, >99.6% with the supermulticoating used by the top brands' top model filters) Hoya SHMC, Hoya HD, B+W MRC and Helipan all offer filters in the >99% performance range. Hoya Digital or Hoay HMC are both 97% performance. And the general wisdom is to not bother with Canon brand, Nikon brand, or double coated, or Tiffen.