Mozilla-bonobo is a Netscape-compatible browser
plugin that uses GNOME bonobo controls to display
content of supported MIME types inside browser
GAI Pal is a dockapp and GNOME 2 panel applet that
gives you a friend that always has something wise
or funny to say.
lookuplet is a GNOME utility that allows you to easily enter search terms (it automatically grabs the X selection when invoked) and then press a key combination which will cause those terms to be substituted into a URL which is launched using your preferred Web browser, or to be substituted into a command line which is invoked. It is rather useful for things like dictionary lookups, Web searches, map lookups, etc. The idea is to shave seconds off of queries that you find yourself doing all of the time. Though it uses the GNOME libraries, it doesn't require that you be running the GNOME desktop environment.
GMatH is the GNOME Mathematical Interface. It currently provides Numerical Python and Yacas with a nice GUI. It also has basic data visualization using the gtkplot widget.