Visual Ruby has a small subset of extended custom controls, that aren't part of the normal Gtk2/Ruby-Gnome2 Toolkit. But, since Visual Ruby builds on Gtk2/Ruby-Gnome2, you can look at the examples for Gtk2/Ruby-Gnome2, and they will work with Visual Ruby as well. There are more things being added to the Visual Ruby core, as well as a new version of the Visual Ruby IDE being developed by me right now, that you can check out at http://bitbucket.org/visualruby/ide
these will eventually be released as gems, as I get closer to getting things stable.
Currently, I'm working on some issues with Threading on Windows, that prove to work in test cases that I run of them, but fails to work in the IDE itself when I run the same code. But I suggest checking out the code, as I'm always working on improving it.