Anything we'll say up until the early 90's or so...any first generation type of rides like the original CBR 600, Original GSXR's, Kawa. GPZ 900, Yamaha FZR line, etc.... You know, the bikes that really started the sport bike revolution.
One of my favorites has always been the original CBR 600's
but my all time favorite old school sport bike would have to be the Interceptor. I'll never forget as a kid watching some guy wheelie one across a bridge near my house.