UV blocks UV light, and was needed on film cameras. You can count a UV filter as a clear filter for digital.
Clear is just that, clear.
Skylight filter has a slight warm cast. It is a specialed filter used for film. You can get the same effect in digital by using software.
A CPL is a circular polarizing filter, used to cut down on glare, reflections off wet surfaces and to cut through hazy or smoggy air. A CPL causes about a stop and a half loss of light, so using it is not free - you may have to bump ISO if you are shooting in moderate light.
ND filters (neutral density are filters which block a certain amount of light (like 2 stop, 3 stop, or 8 stop). They are used to block a lot of light to the sensor so that you can use slow shutter speeds during the bright daylight to get silky water for waterfalls, etc. There are some really cool shots of of the beach wave action slowed down a lot by using an ND filter so look into that if you are doing a lot of beach shots with a tripod.
There are uncoated filters (Tiffen) which are more prone to flare, but are fairly easy to clean. Coated means that it is coated on one side. Multicoated means coated on both sides. You want multicoated for digital since digital is more prone to flare than film was. Some coatings are hard to clean. I find Hoya hard to clean if you get a smudge on it. B+W is pretty easy to clean.
Some filters are made of brass, which turns easier (smoother) than aluminum or other cheap metals, but that is more expensive.
As far as brands, lenstip.com did a test of about two dozen filters, so check them out. I have found that the Marumi brand (found at 2filter.com) is an easy to clean, not too expensive, multicoated brand with good IQ. I have a polarizers, clear filters and ND filters from them. I also have top of the line B+W filters and I cannot tell the difference in IQ between them. However I can tell that some old Tiffen and Hoya filters cause IQ degradation (to be fair, those are older filters that I got second hand - not new).
If you are going to be shooting on the beach, you might look into a lens sleeve (long plastic sleeve or bag) for your camera and lens. You shoot with it on. It protects the camera from salt spray and tiny sand particles. You look silly - but you keep that camera safe! Some of us do not have the money to replace $$$ worth of camera gear if the salt eats it up! And hey, you are going to look silly with a 3 pound black camera hanging around your neck on the beach anyway!
If you do get the camera wet - immediately turn off the camera and take out the battery. Then dry the camera for several days befrore you even attempt to turn it back on. You will also want to clean off the camera/lens with a lint free cloth dampened (not wet!) with distilled water (so that it leaves no residue). Be sure to get in all the cracks and crevices to get the salt out. If you get sand in the lens (gritty feel to the zoom or focus), do not keep using it as the sand will grind the gearing to pieces like sandpaper. Send it in to NIkon for cleaning or repair before you do more damage.
Good luck!
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Catallaxy
