I've been following (and even contributing to) the Padre IDE project from very early on. I've watched it grow from very modest beginings into something quite impressive -- usable, even.
In light of Padre's first birthday, I decided I wanted to give something back into the Padre core rather than just an ancillary project.
I tend to use gedit on Ubuntu, and I rather liked the "right margin" option. This option puts a gray vertical line on whichever column you specify. It's an easy visual queue for long lines. It turns out that the Scintilla editor component supports this feature and all I had to do was enable the menus and dialogs to allow users to toggle the method.
...and there you have it. It didn't take very long, and it's not exactly mind blowing, but it's something I've found useful.