Here is a 1:6 Harley Davidson Fatboy made by New Bright.  I got this bike for my Terminator 2 Arnold custom figure and it kicks some major butt.  It's a little expensive, ranging about $45-60 depending on where you get it from, but it is well worth it.  I own quite a few New Bright vehicles and I love them all.  This particular Fatboy is rather well made.  It has working lights and horns and you can seat a 12 inch figure on nicely and give it a whirl without the figure falling off.  The remote control is pretty sturdy too.  I have not customized this Fatboy because, well, it's simply perfect.  The only thing I could possibly add when I'm in the mood would be two side leather rucksacks or a shotgun holster.