http://railspikes.com/2007/5/14/slider-js-a-javascript-slider-component
http://code.google.com/p/missingmethod-projects/wiki/Glider
I've used it on a couple of sites and haven't had any real problems:
http://www.pricechopper.com/
http://www.dwfreshmarket.com/
but I didn't use the Next/Prev part (wasn't what the client wanted)
Greg