I had a boyfriend once who called it his 'pinkle'. I've never called them anything much (since I find they don't need you to call them by name to respond!), but had to find a term when I had a baby son. I find a lot of the common euphemisms a little distasteful, but settled for 'willie' because it seemed to be what all the little boys around used and it seemed that it would be better for him to be calling it the same thing as his contemporaries.

Love Lynne