With a 100 year-old farmhouse, complete with an ever-shifting fieldstone foundation, we are becoming full-time students of the various theories of basement waterproofing.
One site that we've found that has been of particular help is Basement Waterproofing Pro. It's a good one stop site for pretty much any question we've ever had about interior and exterior drainage. How do you prevent seepage? Is waterproofing the walls from the inside even worth it? etc. Even if you're not going to do the work yourself, it's a great place to get information so you don't get scammed. We've found that everyone we've ever spoken to has a different theory on basement waterproofing and this site makes the most sense out of all of them.
It's not a flashy site, so don't go there expecting flash movies of cartoon people digging sump pumps, but it is a very informative one. There is also a state-by-state directory of waterproofing companies as well as an article on how to avoid getting scammed by shady contractors.
Check out the site here.