When I started this series, I did not think I'd get past 75 to 100 cars/countries. But thanks to the power of the internet, and the help of a few tipsters from abroad, I have compiled the most comprehensive list of presidential/prime ministerial/royal rides anywhere.
Here is the final tally:
S-class: 61
Land Cruiser: 22
7 series: 16
A8: 11
Caddy: 7
Maybach: 6
Suburban/Yukon/Escalade: 6
Mitsubishi Montero/Pajero: 4
Phaeton: 4
G-wagen: 4
Holden-Chevy-Opel: 4
H2: 3
Toyota Crown: 3
Lincoln: 3
Jag: 2
ZIL: 2
Volvo: 2
Touareg: 2
Merc E-class: 2
Lancia: 2
One of each of the following: Hyundai, Skoda, A6, Peugeot, Renault, VW van, London taxi, Daimler, Toyota Century, Hongqi, Bentley, Rolls, Ford Fairlane, Aston Martin, SEAT, Ford Expedition, Nissan Patrol, Stutz, Suzuki, Camry, Toyota Sequoia, Proton, Land Rover, Ford F150, Mitsubishi Galant, Hummer H1, Chrysler Imperial, Mitsu L200 pick-up, Mazda truck, Hyundai Tucson.
Well, the Mercedes S-class trounced the competition, beating the second place Toyota Land Cruiser by a margin of nearly 3:1.
Ratio of cars versus trucks/SUVs: 143:53
Vehicle nationality:
German: 109
Japanese: 37
Other: 27
American: 23
Most surprising: Tonga's London taxi, Malta's Cadillac CTS, Chile's Peugeot 607 (tied)
Most undignified: Thailand's VW van
Ugliest: China's Hongqi

Fastest: Mauritius' Aston Martin DB9
Most pimp: Peru's 1972 Chrysler Imperial

Most in need of bullet-proofing: East Timor's Land Cruiser

Biggest gas guzzler: Zimbabwe's S600 Pullman
CKY
Update 8/5/08: I did a reconcile. Here are the official stats:
Ratio of cars versus trucks/SUVs: 144:52
Vehicle nationality:
German: 108
Japanese: 37
Other: 28
American: 23