August Sandcastle CTP is Now Available
It is still very early in the development cycle, so don't expect a polished product. The sample alone takes 12 steps to go from source code to help file. The Sandcastle Wiki does offer links to open source tools that ease the process, but they need to be updated for the August release.
Though Sandcastle runs on the 2.0 framework, it can generate documentation for C# code based on the 1.1 framework. Scott Hanselman details how to do this on his July 29 blog entry.
Until recently, nDoc was the primary documentation tool for many developers. Now that nDoc project has gone dark, many developers are left wondering what to do with their current projects. Fortunately, Anand Raman does intend to support all nDoc specific tags.