A short tutorial like this cannot possibly cover everything. Luckily, there is a lot more information out there. Here is a list of links that you might find useful (if you have any links that should appear here as well, please send them to tim at centricular dot net).
- Gtk+ API Reference Manual
- Gdk API Reference Manual
- Pango API Reference Manual
- GLib API Reference Manual
- gtk-app-devel mailing list archives - search them!
- gtk-demo - part of the Gtk+ source code (look in gtk+-2.x.y/demos/gtk-demo), especially list_store.c, tree_store.c, and stock_browser.c
- TreeView tutorial using Gtk's C++ interface (gtkmm)
- TreeView tutorial using Gtk's python interface
- Some slides from Owen Taylor's GUADEC 2003 tutorial (postscript, pdf, see pages 13-15)
- Existing applications - yes, they exist, and you can look at their source code. SourceForge's WebCVS/WebSVN browse feature is quite useful, and the same goes for GNOME as well.
- If your intention is to display external data (from a database, or in XML form) as a list or tree or table, you might also be interested GnomeDB, especially libgda and libgnomedb (e.g. the GnomeDBGrid widget). See also this PDF presentation (page 24ff).