Look through the (GUI) Windows Programming FAQ
. There's Tk, Wx, Gtk2, Qt, Prima, Win32::GUI (have I missed any?).
Update: to expound a bit on my limited knowledge of Tk and Wx, IMHO Tk seems more appropriate to throw together a utility with a single or small number of screens (because of the tendency to rely on globals mentioned further down this thread). If I were building a GUI app (something Jouke would know about), I'd probably go with Wx. Gtk2 and Qt are other options that other people like, but I don't know enough about them to have any opinion. Win32::GUI is, of course, only for Win32 systems, and I don't have any opinion on that either. My plan is to eventually try them all. I'll let you know when I do :)