I'm going to give you a basic answer and if you already understand this, then forgive me, but people misunderstand this all the time. The filters for your lens have nothing to do with the focal length of the lens. In other words, it does not matter if your lens is a 35mm lens, or a 27mm lens or a 27-63mm zoom. All of these lenses could take the same filter.

The millimeter size that you care about for filters is the diameter of the front of the lens. Usually it's marked on the front of the lens itself, sometimes next to a circle with a diagonal line through it. There are a variety of standard sizes including 43mm, 46mm, 51mm, 72mm, etc, and there are tons of adaptor rings and other goodies. The easiest way to avoid making a mistake is to take your camera to the local photo shop (preferably a higher end one) and spend some time with the guy behind the counter. These rings and filters are pretty expensive and he or she could save you some money.

Coupla things about filters: if these are for a little camcorder, move cautiously. Light readings are not always taken through the lens and since the meter is somewhere else, it will not compensate for your filter. Also keep in mind that some camcorder lenses back up into the camera. The filter won't let it go in when it needs to, and you could strip the gears of your zoom. Finally, you'll have to turn off auto white balance, or the white balance will balance the color right out of your picture. White balance before you put the filter on, and then the color will show just fine once the filter is on.

A cheaper way to go would be to get a bunch of colored paper. Turn off Auto White Balance. White Balance on a colored sheet of paper. Let's say it's orange. When you white balance on a sheet of colored paper, the camera assumes that the paper is white, and sets the controls to take out all of the color it sees (in this case orange). To take out the orange, it adds the opposite (kind of a blue). Your whole scene will appear to be blue, and you won't need a filter. Here are some opposites to start with: Red/Cyan (kind of a sky blue), Green/Magenta, Blue/Yellow.

Good luck.