Maybe it's my 27 years as a professional chef speaking, but I have seen more knives ruined from the result of belt type sharpeners than I can count.
Belt type sharpeneers generate an enormous amount of heat and friction on the edge of the blade removing most, if not all of the tempering from the steel. Yes, they will sharpen the knif but now you will be "stuck" sharpening that knife very frequently to maintain that edge.
Like cleaning a gun, there are no really good shortcuts, both are laborous jobs that require time, dedication and simple tools.
The Gatco/Lansky style tools work for their intended purpose on smaller pocket knives as they have built in angle guides but are more difficult to use on longer kitchen type knives.
My suggestion is to buy 2 stones; one double sided coarse/medium grit stone and one "Japanese water stone", the latter will be slightly pricy but I have had mine almost 11 years (if you do the math it is really cheap, years/dollars)
I would caution everyone against using oil, I know it has been the norm for many years to many people, but consider what the oil is used for>a lubricant, and to "float the metal shaving from the stone"
My suggestion is to use a cup of tap water with a teaspoon of dish detergent in it. Not only will this do what the oil is supposed to do it will also preserve you stone and keep it clean.
If you have a stone that has become "slick" from oil build up and metal filings spray it with "Easy-Off" and let it sit for about 30 minutes and then wash it with really hot soapy water and a brush.
The Japanese water stone can be found at: water stones

Method: Optimum angle for a slicing knife is 17 degrees/ side. but no matter the angle try to do both sides the same.
With the stone lying perpendicular to you and holding the knife by the handle with the piont facing away from you, make 25-50 strokes of the same motion on one side of hte blade(depending on how dull the knife is); turn it over and repeat the same process.
Start wit hthe most coarse grit and work to the finest grit, all the while keeping the stone saturated with the soapy water. (if you need to angle the blade slightly to keep from hitting your knuckles on the stone, so be it)
Hint: soaking the stones in the soapy water ahead of time for a couple of minutes make the job slightly easier.
When you get to the Japanese water stone you will find that the edge is actually becoming polished as well as sharpened which helps maintain the keen cutting edge well past what would seem "normal".
I would never use these carbide sharpeners as they create a "cutting"edge that is parallel to the blade which, again, may appear sharp for a period of time but will constantly have to be "honed" to maintain any kind genuine edge.
I have more info but my hand are cramping from typing[:@] I could go on all day about knives

mlaubner gave some very good advise. The only thing I'll add, is if you don't want to spend the money on the Japanese water stone, a good ole Arkansas stone will do the trick and is much cheaper. Another thing to think about, is the hardness of the steel that you are trying to sharpen as well as the quality. I have a Buck knife that has some extremely hard steel and if I put a coarse stone to it, it will never get sharp. I usually use a medium to fine stone then go to the Arkansas stone and she'll hold that edge for quite a while. Stay away from the belt sanders and the grinder type gimmicks, as stated before they generate too much heat. Another tip for some of you that may have collected some used knives that have lost their temper, get you wife (or you) to bake a pan of cornbread when she removes the cornbread from the oven, stick the blade into the cornbread and leave it there until the bread and blade cool. This will retemper the steel in the blade and it will be able to be resharpened.

i have a little "gismo" called an accusharp i found it in a local tackle shop and its just one of them you drag over the blade and it has 2 pieces of carbon or something inside shapped like a V and it does great for me it puts on an awesome edge but ive about wore it out all my friends have bought them to since i showed them mine it was only like $10 or so but its great if you cant use a stone ive destroyed more knives then i care to mention with a stone and im just really bad with them but that accusharp thing works really good and i was impressed with the edge it put on my knives and i have bald spots on my arm and cuts on my fingers to prove the edge it`ll put on a knife

I would also like to mention that you can make an inexpensive, yet very effective sharpening "system" from a couple of sheets of , progressively finer, wet-r-dry sand paper, the type used for body/metal work.

Find a couple of nice boards, glue the paper onto the boards, wet down the working area of the paper and have at it.

For years, when I was on the "trade show" circuit, I would just pack a "multi-pack" of this stuff in with my knives and luggage to keen up the edges of my knives.
I started with 440 and worked up to 660 or 880. Just a few strokes on each side does the job. When I traveled I would just put the paper on a really flat table and go from there.
It is economical and really does a great job.

I have cut thousands of salmon and halibut as well as my share of elk, deer etc. I found a long round diamond to set the edge and a steel to lay down burrs is fast and best for me. I tried the carbide things but they will knock out small pieces on the edge of a thin blade fillet knife and ruin it.

Firestone Broadhead Sharpener. Cheap, light, very easy to use, and puts a razor sharp edge in less than a minute. Use it once and that old wet stone will seem more useful as a paper weight.

I use Japanese water stones, all the way up to 8000 grit if I feel like it. Normally, however, I'll stop at 4000. If I need to establish a new bevel, I'll use the Gatco, but I always put the final edge on it with the water stones. Sometimes I'll finish with a strop.

8000 grit...it's not only sharp, it's polished

My two cents....All i use is a good stone, water or oil, and only when it needs a new bevel, ussually all the blade needs is a ceramic croc stix, it has the angles all set up and if you hold the blade stright it does the rest, i dont concider a blade sharp till you can shave the hair on your arm with it and the croc stix work well. I will add that you need to have a knife made with decent steel first though. You cant get a good edge on bad steel, if it's made in china for 1.99 dont waste your time.

The Lansky system works for good for me although it is difficult to use on the long blades as mlaubner mentioned.