MLB.com had a recent article about undrafted Major Leaguers, and they mention the independent baseball leagues as a part of this process:
The article talks about George Sherrill and Daniel Nava as primary examples of players who started in the independent leagues before making it to a Major League team. What is also interesting is that MLB.com actually discusses “gaps” and “cracks” in the scouting process used by MLB teams. Although some players who were overlooked in the draft ended up getting signed by affiliated teams, it is always inspiring when MLB talks about the independent baseball leagues in a favorable light.
There are several good books about the independent professional baseball leagues. You are welcome to see a list of suggestions through this link: Books Get notified of upcoming independent baseball tryouts from either of these services: first service or the second service. Prospective players can find some helpful resources here We will be providing a growing list of possibly helpful tips and suggestions on various baseball information. This will range from "how to" information about baseball skills all the way to helpful information for casual baseball fans. Please click the link for more information: Tips And How To Information