For the Ducati brand the "R" version is their full on race inspired bike with the upgrades and different exhaust system and is usually not street legal. The "S" has some of the upgraded parts, usually brakes and possibly coated forks. The regular version is just designated by the number such as 999, 748, 1098 etc. The latest top of the line sportbike from Ducati is currently the 1098, though the 1198 is coming soon.