Australian company Eye See Data has produced a brilliant chart documenting international football transfers since 1900/01.
They then produced a video cramming all the transfers into a 60 second visualisation, highlighting the explosion of transfers in the last 10 years (with 75% of all transfers taking place in that period), as well as showing the extent to which Europe dominates world football.
Check out the interactive chart below for a more detailed look at the data. (Full sized chart here)
H/T 101GreatGoals