I have done this mod on 4 bikes and there are a few different ways of going about it.
1.) Kimpex Unit. Cheapest, but throttle hand gets warmer than the other hand unless you insulate the other grip a little. The 3 way switch is big and cheesy, as it was meant for a quad or snowmobile. Cdn tier has them for about 20 bucks. I use the elements and then toggles from radio shack or whatever the hell they are called these days.
2.) dual stars. $$$ but very nice, as Borat would say. Aerostich has a set too but haven't looked at them.
3.) Hot Grips. I havent used in a while but they were a full sleeve that replaced your stock grips. Hard rubber and not my cup of tea. I like the kimpex coz they use the grips you like.
4.) Combo #4. Kimpex elements and switches from dual stars. Computer controlled heat, both hands are same temperature.
www.dual-star.com/index2/Rider/heated_grip_kit1.htm
www.hotgrips.com/
search.aerostich.com/search?ie=&site=my_...tatic&q=heated+grips
news.motorcycle.com/article.motml?thold=...lat&order=0&sid=2538
