The current project in the UserInterfaceDesign programming course I'm taking involves creating an interface using Python's bindings for wxWindows ?, called wxPython (http://www.wxpython.org). Kind of cool, since it's cross platform, etc.
Still, it's Python, not Perl which is obviously my favorite. Lately I've been using NTray, one of the extras that are linked to from Nagios's download page. Basically it's a simple little Perl application that has been compiled to an EXE using ActiveState's Perl compiler. It sits in the Windows system tray, and periodically monitors Nagios' CGI scripts. Based on the status it sees, it changes its icon from green to yellow or red. It's only 734 lines of code, but has a nice configuration dialog to change various settings, uses XML to save data too, and so on. It's using Win32::GUI ?. This is really a nice Object Oriented layer that sits on top of the Windows DLLs, using XS to glue things together. Beats using direct Win32::API calls.
I'm tempted to start using this for creating various tools... it's a very small step from a lot of my command line scripts to add a simple GUI on top.