"Childe Roland to the Dark Tower" by Harlan Elam - Hero Complex Gallery
From Tessie Girl: "The Stephen King Universe Flowchart Update (including the Dark Tower Series)" -- Click through for a larger version or to purchase this amazing chart as a poster.
Dark Tower - The Dark Tower Wiki, Dark Tower Map. Once she started chemo though I just put the series down. She loved those books though so I may well start reading them from book one again.