While you many not need a special device to do Kegel exercises many people find using something like a sex toy or other exerciser makes Kegels easier to do and more effective.
There’s also the fact that most products for Kegel exercises double quite well as a sex toys and can be used not just for sexual health, but sexual pleasure as well. The products below were either designed specifically for Kegel exercises, or found by many to be helpful enough that they've developed a reputation as kegel exercisers.

BabelandOne of the first cylindrical products designed for Kegel exercises the Kegelcisor is perfect for exercising your PC muscles. It is made of surgical stainless steel and is heavier on one side than the other, plus has three balls along the shaft for doing squeezing exercises. It can be boiled in water and won't ever wear out. The Kegelcisor also comes with suggested exercise routines for doing kegels.

BabelandA set of three PC muscle exercisers, each with a different shape and weight, makes it easy to measure your progress with both strengthening and resistance exercises. Made of silicone and ABS hard plastic, designed and manufactured by the people who brought us the G-Ki and the original Je Joue, the Ami is more of a committment than other toys, particularly because they are much less multi-purpose, and more focussed on exercises not pleasure. But if you're looking to exercise your PC muscles, Ami likely won't disaapoint.

Image courtesy of Come As You AreIf you're looking for function with a bit of style, the Energie may be worth considering. It also comes with some weight to it (but it is made of a coated heavy plastic, not metal) and has the traditional two sizes of balls on either end, but is designed to be a little less clinical looking. It is also a little less expensive than the stainless steel products.

Image courtesy of Dodsonandross.comSex activist,
masturbation pioneer, and author of
Sex for One and
Orgasms for Two Betty Dodson has designed her own device for doing Kegel exercises called Betty's Barbell. Made of stainless steel, like the Kegelcisor, Betty's Barbell has a shiny finish (so it looks a bit sexier!) and a slightly different design, with three rings along the shaft in between two different size balls on either end.

Image courtesy of BabelandEarlier versions are known as Ben Wa or Duotone balls. This modern version of two round balls (each with a metal ball inside), made for vaginal insertion, is coated in a safe
elastomers material which is durable and easy to clean. Simply holding the balls inside as you move around requires you to do a mild Kegel exercise. Plus you can also insert one ball and squeeze down on it as a strengthening exercise.