Pick your poison:
1. 2005 Audi A8L W12, 97K miles - $18.5K
2. 2006 BMW 760Li, 92K miles - $18.9K
3. 2005 Mercedes-Benz S600, 80K miles - $15.8K
Interesting how the Audi and BMW models hold their value a little better than the Mercedes overall. The Mercedes also seems to be the most plentiful. There are about 100 used S600s for sale on AutoTrader, vs. about 50 760Lis and only 30 A8L W12s.