Metz 150, Avon Cobra 150, Michelin Commander II 140... I prefer the smaller tire as it provides an immense improvement in turn-in, low speed steering and overall handling, plus it makes the big girl feel about 150 pounds lighter than she actually weighs.
Note: I currently run a matching Exedra Max 130/70 ZR17 in front, but that is not compatable with ABS brakes or, reportedly, with the Roadster's different front peg placement.