This page lists a number of lawsuits and settlements which relate directly to web accessibility. Each case is listed with its plaintiff(s), defendant(s), the year in which it occurred, and an URL at which you can find out more details. This list may already be out of date. I’ll try to keep it current.
Update: This is now being driven by a Github repository I maintain at: https://github.com/karlgroves/a11y-lawsuits