I am involved in a project with two other people who are developing a web proxy script with more features and functionality than other scripts. One of them is a member here (R4z0r). It's unfortunate that some of the great ones we know are not always maintained. It will have an independent theming system and a comprehensive but easy to understand admin panel.
One of the main features behind this is going to be central deployment. This is a feature for webmasters who operate several proxy sites, as many do. You can easily change the theme or settings of one or several sites in just a few clicks.
You've all been asked this question before, but what features would you like to see from a web proxy script alternative?