Interesting tid-bit:
Most of the variability in which side your penis hangs to is due to assymetry in the length of the right and left corporeal bodies (the "cylinders" that make up the shaft) and since this is random in the population, you should expect to see an even distribution between right and left. But the reason that more men's penises hang to the left than right is due to the anatomy of a vein way up in your abdomen, near your kidneys. In the majority of men, the gonadal veins (which drain blood away from your testes), follow different paths. The right gonadal vein (from the right testis) drains directly into the inferior vena cava and experiences very little resistance, while the left gonadal vein (from the left testis) drains into the left renal vein. As a result, it experiences more resistance and impaired flow compared to the right. As a result, the left testis hangs lower and slightly further back (some of you noted this in your posts) than the right, allowing the penis to rest slightly to the left (it'll hang wherever there's space for it). This is also the reason why varicoceles (basically varicose veins of the scrotum - feel like a bag of worms when rolled between the fingers) are more common on the left than the right.
Hopefully that was somewhat enlightening :)