Linux/Windows: Based on GRUB but many shades beyond it in the looks department, Burg is a quick install for Linux users that lets anyone theme their multi-OS selection screen, or customise their own theme. It's becoming install-ready on Windows and Mac too.
At the moment, those comfortable with compiling a Linux app on their own, or even compiling Windows code, can install Burg on their own. For the rest of us, the easiest means is explained at the Ubuntu Wiki, with just a few commands to enable a repository and install the necessary packages. Once it's installed, you can press a few keys at boot-up time to quickly change your theme or resolution. To change the available options and wording, you'll need to dig a bit into Burg's text configuration tools — though some themes offer their own windows and helpers in that area.
I installed the screen seen above on my own Ubuntu partition in about five minutes — the extra Ubuntu options offered are memory tests and command-only options I intend to remove. Reader Mujitaba Meher, who tipped us to Burg's slickness, posted this screenshot to show another way you can go:
Burg is a free download, most easily installed on an Ubuntu Linux system, but available elsewhere.
burg [Google Code]