I am often asked what sharpener I recommend.  The answer depends on the working style of the person asking and what they are willing to spend.  Following are some recommendations, sorted by price with comments on each model:

For under $20:

A good bench stone and time to develop sharpening skills. Not as good as a guided system, but definitely the lowest price.  For the Luddites.

For about $75:

Spyderco SharpMaker - quick and easy, but bevels are not pretty.  Handy for the kitchen, and recommended for people who don't want a lot of work, but don't want to spend the money for an electric machine.

Lansky or GATCO or DMT rod-guided system - not as fast to use as the Sharpmaker, but nice clean bevels.  For the craftsman.

For around $150

Chef'sChoice 320 ($90) - electric machine, sharpens and strops to a shaving edge.

This or the following CC model is a perfect, no-skills solution for those willing to spend the money.

Chef'sChoice 120 ($120) - adds a coarser "pre-sharpening"  stage, needed for really dull knives and/or thick blades .

Chef'sChoice 130 ($130) - adds a "steel" stage in place of the second diamond grinder.

EdgePro Apex ($165 to $245) - the perfectionist's rod-guided system.  See below for Pro model.

Paper Wheels ($70 for the wheels, plus $50 for a bench grinder).  Requires a little skill; angle control is manual, but it is the fastest way I have found to sharpen a knife.

For around $500:

EdgePro Pro model ($375 to $650) In addition to knives, accepts attachments for scissor and chisel sharpening.

Chef'sChoice 2100 commercial sharpener.  This machine produces a double bevel edge, unlike the triple bevel produced by their home machines.  The sharpening unit is removable so it can be cleaned in a dishwasher, and be replaced when it wears out.  Life expectancy is about 3000 knives.  About $379 for a setup with signs, etc.

For around $1000:

Tormek - power wet grinder with fixtures available for everything including scissors and woodworking tools. Angles are well controlled and bevels are clean.  Can also be used freehand.

$750 will equip you for knives and scissors, but you can spend up to $1000 with all the woodworking fixtures.  Buy the stone grader and stone truing tool.  It is a travesty that they sell it without them.

For around $2000

The F. Dick sharpening machines, SM-110 and SM-111, are worth considering for someone setting up a sharpening business.