The AccuSharp 001 might be the last knife sharpener you'll ever buy, and it only costs $8 as an Amazon add-on item. All you have to do is run it over a blade edge two or three times, and you'll feel like your knife is new again. It's trusted by America's Test Kitchen (scroll to the 2nd entry on the list), so you know it's good.

The diamond-honed tungsten carbide sharpener inside the handle typically only has to be changed out once or twice a decade (they can be reversed for even more longevity), and the unit as a whole is sturdy enough to withstand years of abuse. It even works on serrated edges as well as straight ones.

You don't need some fancy knife sharpener that costs in the hundreds of dollars. If you're already going to be buying at least $25 worth of stuff on Amazon, toss the AccuSharp 001 into your cart and thank me later.