I like the Harley idea, myself.
For my 50th, my wife did me something I considered pretty special. As we are NASCAR fans, she bought me one of the Buck Baker Driving School experiences down at Rockingham Speedway. I got to drive a Sprint Cup Charger that used to be one of Rusty Wallace's around all by myself, after some coaching that is. That was something I'll remember forever.
Proves that a great gift doesn't have to be something material. If it comes from the heart and leaves a great memory, you can't ask for a better gift than that. Sometimes, those are the best ones.