My wife has toyed with rding a Ridley but they look a bit cheaply constructed to me. She has also liked the Sporty Nighster. I would buy her anything she wants but I think all she really wants is to give me a neck rub at 75MPH. :-)
My wife started on a Honda 550four, then a Ninja 250 then a Hayabusa then a Nightrain. Now she decided its just as cool to have a 350z Roadster and ride on the back.
Her first & current ride is a 2006 Suzuki Boulevard C50. She's put 12,000 miles on it in 2 years. It's a great bike and I steal it for a ride every time I can.