From a fans point of view, the Valley League and Cal Ripken League offer some excellent summer college baseball. My business travel affords me an opportunity to catch a game every so often. I'll check-in on my son's college teammates in action, and folks that I know. D1, D3, JUCOs schools are very well represented.
As a matter of fact, a few weeks ago Swampboy and I caught the Cal Ripken Summer League All Star game where his son pitched lights out in middle relief. Incidently, the starters from both teams were D3 kids.