yup CPL will do... imho when you are able to fully polariser the sky, dynamic range normally ain't much of a problem liao (other than some clouds detail lost, others should be fine), but adding a GND will make it very dark blue.
That's a photo I had taken during my trip to Yunnan.
I have observed that the sky in photos seems to come out bluer in those places of high latitudes and/or altitudes.
That said, it is possible once in a while in Singapore to get bluer than blue skies if lucky to be in the right time and place... for example this was taken with a Fuji F30 without the aid of a polariser, ND or GDD. :dunno:
Megaweb has given some good advice. To add - know the time of the year as well.
Another thing required is to get your basics right. Use of aperture, shutter, exposure, metering. I shudder to hear some jokers claim that they need wide-open f5.6 on a bright sunny afternoon at 4pm, 1/125 at ISO400... without using filters.
Adding equipment is a stop-gap that may work for limited conditions, knowing your basics can get you good pictures almost all the time.
This link has photos which are exclusive from Singapore. No filters were used. Some were even taken with circa-2002 digicams. No PSing either. All are out-of-camera shots, whether you wish to believe it or not.
My "circa-2002" means the digicam was what I was using in 2002/2003. I usually do not bother to mention the make/model of the camera nor the lens used because those are minor and non-consequential factors in producing a decent photo. At least IMO.