Point of clarity: the Application Manager only displays packages that are in the "user/*" categories, of which there are only the 4 in repositories.maemo.org, but there are also plenty of other packages (e.g. ssh) that are not in a "user/*" category. Most of these other packages, however, are not useful to users as graphical applications and are more useful to fill dependencies (or for command-line apps).

There are other repositories mentioned in the ApplicationCatalog2006, including ones for FBReader and Maemo Mapper.

Other ITT posts have also referenced repositories for gaim (see this page) and for GPE PIM (see this post).