Over an average of 40 studies conducted internationally in the past sixty years or so, 93% of men surveyed had a penis with a length of 5 to 6 inches, and a girth of 4 1/4-7 inches. Half of the men had a length between 5 and 6 inches, and a girth (the measurement around the shaft) between 4 1/4 and 5 1/14 inches. Since most of these studies used volunteers, the average size probably skews a little higher than average: who's going to march into a study with a small one?
On average, Africans do have larger penises, Asians have smaller penises, and Caucasians are around the middle. However, this is mainly due to average overall body size: Asians tend to have smaller bodies overall, while Africans are the largest. Overall, there is no difference in penis size between men who have the same height regardless of race. Even if you don't take this into consideration, the overall difference in length is less than an inch.
Brooklyn resident Jonah Falcon has the largest penis ever measured at 13 1/2 inches; he was the subject of a documentary on penis size made by HBO in 1999. The smallest recorded penis is 2/5 of an inch, although there is no name associated with this record holder. (Wonder why?)
These women go into a little more depth. Even though they're just talking, this is probably NSFW:
Posted 2004 day ago