I put together this visualization of the transfers that have occurred between Premier League teams in the past 21 years.
The chart shows first the amount of money moving between teams. You can see, for example, Liverpool has profited immensely from transfers. Their biggest trading partner in terms of money is Chelsea, which is no surprise since Chelsea paid £50M for Torres in 2011 (in total Liverpool has made £70M from deals with Chelsea).
Selecting the "count" view will show the number of players transfered between teams. This shows that Tottenham, Blackburn, and Newcastle are the three biggest feeder clubs. That is, they move the most players to other Premier League teams.
The visualization only shows teams that are or have been in the Premier League for the past 21 years. Of course, most transfers involve teams that are not in the league. These are not currently represented. Only transfers between two current or former Premier League teams are shown.
I scraped the data from http://www.transfermarkt.co.uk/.