Question of the day: Is penis length correlated with hand size? The truth is that I don't know, but I would guess it is. If I'm not mistaken, some of the same genes that control limb growth also influence genitalia growth. The 2D:4D finger ratio is not really relevant because it measures the relative size of fingers, and is of questionable validity.
Lee Ellis published a fascinating paper which lists traits that are positively associated with penis length: masculine mannerisms, masculine body build, physical strength, strength of sex drive, low-deep voice, upper body strength, lower body strength, and amount of body hair. The argument is that all these traits are influenced by testosterone. The main weakness of the study is that the data are self-reported. Rating your own penis is like asking students to grade themselves.
I can't recall the paper, but I do remember reading about a positive correlation between height and penis length as well. Again, the idea was testosterone.