PostgreSQL manual consists of the 1351 topics (and still grows!) and I don’t like the search engine on the site much. It is also worth noting that the tree of contents (TOC) in CHM version speeds up navigation a lot!
A good friend of mine Edward Smirnov obsessed with creating a utility capable to compile the manual in CHM format using a set of HTML / SGML files shipped with PostgreSQL. He managed this! The only thing missing is the Index support (HHK file in CHM archive).
However, even without this feature such manual a hundred times more comfortable for me than the online counterpart. Especially I’m excited about lightning full-text searches.
UPD By default Windows doesn’t allow using .chm files downloaded from Internet. So you should right-click on the .chm file, then Properties and then check Unblock checkbox (or Unblock button in Windows 7 and older).