Can you imagine opening your friend's fridge and seeing a row of chocolate DONGS?

That would be cool...

The OED gives equal weight to the two spellings, but I think that "willy" is superior. I write with the authority of a second-place finisher in a local adult spelling bee.

See also Shakespeare's Sonnet CXXXV, in which that vile horndog writes, "So thou, being rich in 'Will,' add to thy 'Will'/One will of mine, to make thy large will more." "Will" was used to denote sexual passion in those days--I'm of the opinion that the first uncapitalized "will" probably refers to Will's willy, the introduction of which will increase his lover's ardor. Combining my theory with the ever-popular queer interpretations of the sonnets (not that their queerness always requires much interpretation), I start to wonder whether the sonnet is addressed to a man, and if Will's willy will combine with his lover's especially "large will" to make a tantalizing "more."

Oh my lord! Sonnet CXXXVI is hilarious in this regard. "'Will', will fulfill the treasure of thy love,/Ay, fill it full with wills, and my will one." Is Shakespeare proposing to pimp his paramour?

I once worked in a record store that sold pipes and bongs including a dildo model painted gold and about ten inches high. It got no end of comments and attention from customers, but the sole person to ever buy one was someone who needed it for a bachelorette party and tried to return it afterwards. (We told her no, even though it had been wiped dry of saliva.)

I would say "willy" myself. I usually defer to Roger's Profanisaurus for this sort of thing, but it is unfortunately not listed.

Willy, indubitably. Willie is a man's name (so is Willy, but only in Deutschland).