GKSu is a library with a Gtk+ interface that allows su and sudo to be operated through it.
One of the best things about GKSu is that it's constantly being updated. In fact, the latest version of the software, 1.3, comes packed with some new and exciting features. For instance, it's now the first high-profile stable release of the gksu application. Additionally, it now comes with changes in libgksu, which means you can use a global gconf setting to use su or sudo as the backend.
Perhaps more importantly, the new updates also make it easier to handle "wrong password" issues. There are other additions as well, with the most notable one being the optional nautilus addon. This feature adds an "Open as administrator" menu item to the nautilus context menu for various files and folders. It's important to note that this menu item will open that file using the application that handles its type by default using gksu.
Overall, if you're looking for a reliable Gtk+ frontend to su and sudo, then GKSu might just be the perfect solution for you. With so many new and exciting features packed into one application, you won't be disappointed with what it has to offer.
Version 2.0.0: N/A