Photographing sunset or sunrise using a DSLR camera.?

You don't necessarily need any filter. And you definitely don't need a polarizer since the CPL has zero affect when shooting into the sun or when the sun is 180 degrees behind you. CPLs work best when the sun is at a 90 degree angle to your subject (overhead). Their effectiveness of removing glare diminishes as the sun get lower in the horizon.

If you want to force the camera to use long exposures to blur motion such as water or clouds, then you need a neutral density filter. I own a 6 and 10-stop ND filter, but really only use the 10-stop filter.

Instead of filters, you may find shooting sunsets using high dynamic range (HDR) techniques to be a great solution. Problem with sunrise/sunset shots is that the brightness range is beyond what cameras can capture. If you expose so that the highlights aren't blown out, your shadows are too dark with no detail. And if you expose for the shadows, then your highlights are blown out with no detail. And a shot in the middle will leave you with no detail in either the shadows or highlights. However, using HDR software allows you to take those three shots and blend them together to make one image with detail throughout the image. Good software for this is in Photoshop CC, there's also Google's Nik software that is a plug-in for Photoshop. There's also Photomatix.

Only photograph sunsets and sunrises when conditions are such that you do not need a filter!

"Conditions right"? When the sun is very near the horizon, and thus not too horribly bright compared with the remainder of the scene. Indeed, as Keerok implies, you need to consider exposure level, and might indeed need to set a degree of "underexposure" if using Auto Exposure. But at least with digital you can see the result straight away.

Just possibly a graduated ND filter might help darken the sky in some sunset scenes.

What type of effect are you after ?

What are you hoping to achieve ?

Personally I haven't used a filter for that kind of shot, never needed one.

Some photographers might use a graduated filter to achieve a particular effect, its an awkward question without more background info, pop over to the 'Cokin' website they produce filters and you could ask for a catalogue to be sent out (would help you see what the different filters do and what's available).

Apart from that some photography guide books cover the subject and You Tube might have some guides and tutorials.

You don't need a filter to photograph a sunset or sunrise.

No filter at all.

Reduce the meter recommended exposure by 1-2 stops (experiment to get the best)

Consider increasing saturation.

Consider tweaking white balance during post processing to intensify the red/orange.

You don t really need a filter, unless you want to balance the sky & foreground exposures, in which case you might want to use a grad ND filter.

Otherwise, just shoot manual, spot meter on the area you want to get rich colour & stop down 1/3 to 2/3 stop.

use shutter speed as S on your camera fast shutter speed made darker let camera adjusting you diaphragms A

Underexpose. Swing exposure compensation to the minus side.

You don't need a filter :)