Eagle1 Wheel Cleaner, and Westley's Bleche White for whitwalls
Just about any of the "spray on, hose off" wheel cleaners in the auto parts store will do a good job. Definitely get a wheel brush to get into the small places, and around spokes. Once they're clean, put some type of polish on them so they stay clean, and/or are easier to clean the next time.
Anyone who has scrubbed whitewalls knows what a PITA it can be. Get yourself some Westley's bleche white in the spray bottle. simple spray on, and wipe off (NO hard scrubbing) will get your whitewalls sparkling clean with little effort.