i use a spray bottle of an automotive version of simple green and a medium stiffness brush. i have used kerosene once without any ill effects.
i have found two tricks to keeping the rear rim relatively clean. use a chain lube that doesn't fling all over the place. and clean it every time you wash the bike. (duh.) i used to skip the rear rim once in a while when using motul chain lube and when i did wash it it would be a huge project because it would be so dirty.
but thanks to the black rims of the '05 i can let it slide once in a while if i'm in a hurry.
Go to the automotive section and get those baby wipe like cleaning things. They work so sweet. Ypou'll be amazed. Armor-All makes some in an orange container and they work good. The best ones I have found though are made by Zep in a blue container. I got them at the dollar store. Can't find them anymore though.