Do I need any kind of filter?

I shoot Nikon and have an 18-200mm and in a couple days will also have a 50mm 1.8d. What are the most common filters, and what are they used for? Are there any that I should have for my lenses?

Added (1). When I'm searching "67mm UV filter Nikon" on Google I'm getting a very wide range of price results(from $8 to over $30), why would this be?

The only filter you really NEED would be a quality UV filter to protect the delicate front element of each lens. For the 18-200 (if it's a Nikon) you'll need a 67mm and for the 50mm you'll need a 52mm. I won't leave the house without a UV on every lens in my bag.

Mount and keep on any UV filter on each lens. Other specialized filters you might consider would be a circular polarizer or a neutral density filter. The polarizer removes glare from water, glass, and all non-metallic objects and can also increase the color saturation in the sky and on water. The neutral density filter can allow you to use wider apertures for better bokeh when you're shooting in very bright outdoor lighting.

I disagree. In speaking to a camera repair man he said he has had more jobs removing dented filters stuck on the lenses of cameras. If you put cheap glass in front of your lens you might as well have a cheap lens, that's old school. I would suggest using your sun shade to protect your lens. A polarizing filter to eliminate reflections in skies, on leaves, water, etc and if you want to shoot long shots making water silky some neutral density filters. If you are big into landscapes you might want a graduated neutral density filter. With any filter, get the best quality you can.

UV filters are useless. They are nothing more than an insurance policy for the clumsy. A lens hood is what you want to protect the front element of the glass. And they cut down on glare from unwanted light entering the lens, which is what some UV filters claim they do, when in reality, all they do is make your images dull and flat.

As for filters you should invest in are a GOOD circular polarizer and a series of Neutral Density filters.

It is essential that you don't cheap out on this. A cheap filter will make a cheap lens out of one of even the highest quality. Save your pennies for a little while and get the good ones. Cokin is my brand of choice and although certainly more expensive, they are a great tool in my camera bag that when used properly, add a great enhancement to my photography.

Ignore UV filters, your sensor already has a UV filter on it.

What filters do you need? Depends on the type of photography you do. I just shot some shots and the model wanted to go into the water. I could have used a polarizing filter for those shots but I don't own one. And filters are good for blocking out the sun when you want to play around with long exposures or wide aperture shots. Gradiated filters are good for evening out exposure between the sky and your subject… It depends what you want to shoot.

I agree that UV filters to 'protect' your lens is unnecessary. The reason I feel this is: when, really, would you need to protect your lens element from something? Are you shooting in a sandstorm? I don't know about other people, but here's what I do when I'm out shooting.

1- See something that inspires me to take a shot.
2- Take the lens cap off and shoot.
3- Replace the lens cap and keep walking.

So when and from what does the lens need 'protecting'? I'm extremely tough on my gear, shooting in deserts, forests, cities, mountains, beaches, heat, moisture, dust, poking the lens through foliage, crawling across the ground, holding my camera out the windows of moving vehicles, and generally ignoring most safety precautions to myself or my gear, and I have never scratched or damaged anything (except my limbs). I'd be more worried about my camera hitting something and breaking the UV filter, driving shards of glass across my lens.

But to answer your question, a circular polarizer is invaluable for cutting reflections, shooting through glass or water, intensifying colour, cutting haze, deepening skies, etc, as well as an 8-stop regular and for slowing shutter speeds or using wide apertures in bright light, and I also carry a Cokin holder with couple of graduated NDs for landscape work (and a reverse grad and, but that's just me). That's all you need unless you want to get into infrared or something. Technically, you don't 'need' anything- but a polarizer at least is pretty universal if you plan to shoot outdoors.

Some people buy larger filters and use a step-up (adaptor) ring. This will do two things- allow you to buy wider lenses at some point without also buying new filters, and also cut down on any darkening of the corners (vignetting) that can happen with thicker filters at wide angles.