My uncle just got a lead on a 2002 black on black S430 with 30k miles going for $15k. Supposidly it even has a couple more years of warranty left.
My dentist has had great luck with his 2000 S430, and another RE agent I know has a 2001 which has been good...well except when she hydro locked the motor.
Other than that self induced issue its been a good car.
W220's are not the best S class, but they sure as hell are one of the best driving. Thats a lot of car for $15k.