Glade 3

One of the things I've always hated about GTK (and development with it) is the travesty that is Glade. No undo, unintuitive layout, generation of files that don't actually matter, C-specific stuff that's deprecated and useless. I've tried other UI builders (stetic and gazpacho) which were better, but still far from perfect.

Recently, though, I came across Glade 3. It's not quite ready yet (it's still CVS only), but it's a VAST improvement over previous incarnations, and I would recommend it to anyone who currently uses Glade 2.