Here are two books that were quite influential for quite a while. They speak, from the lives of two missionaries, of the extraordinary spiritual fruitfulness that God gives in response to prayer (John 15:7). Yet I would say that the names of Praying Hyde and David Brainerd are practically unknown to most modern evangelical congregations.
Here are the links to the Google books releases of these books. The book Praying Hyde is also available as a .PDF, which can easily be downloaded and read.
CBN also had a short feature on Praying Hyde: Profiles In Prayer: Praying John Hyde By Richard Klein. Wikipedia also has short articles on both: John Nelson Hyde and David Brainerd. These would be more for background information in preparation for reading the longer works.