I am not sure what you mean, is it cleaning the rim like in washing or cleaning the braking surface. I will discuss both, here goes:-
1. Alway use low pressure water. Water that enters your bearings WILL cause eventual damage that can be expensive. (this includes the headset, bottom bracket and wheel bearings) Use a long handled brush and a sponge or cloth with youe car wash or bike wash detergent in hot water. Wash the rims and then the spokes and hubs. Dry with a cloth or blowdry with your vacuum cleaner blow function (this works very well)
2. The braking surfaces of your rim are normally machined and should run true. Use a 3M plastic sourer sponge and clean the aluminium lightly with this. It will remove all the accumulated rubber form the rim. At the same time inspect for dents, burrs and other defects. Contact your LBS for work on these defects. Mavic also makea a hard rubber eraser that you can use.
Hope this helps and keep those wheels spinning!!!
Got to love these ancient threads, where the OP asks a short question, we get into long and heated debates for pages and years, and he never comes back. Alcohol seems to work just fine for me for the infrequent cleaning of the rim sidewalls. But I like the updates here.....gasoline and water cannons are both great suggestions for cleaning bikes.