Linux only: GeeXboX has finally released a stable version of their new interface called Enna. Used with GeeXboX or as a standalone application, it handles all your music, photos, videos and even ebooks — with style.
Enna features a very attractive interface, with direct access to all your hard drive's media in a very user-friendly way. It even automatically fetches covers, fan art and information for you — and you don't have to switch in and out of a "Library Mode" to see them, making navigation a bit nicer than some of its competitors. It's also added books as a medium — and while one may wonder who would want to read books on their television screen, comic books are another matter. Enna currently supports GoComics and OneManga as content providers, meaning you can read your favourite comics in a whole new way.
Other than the bookstore, though, and an arguably more user-friendly interface, Enna is still relatively young, and it's missing some of the more advanced features, such as UPnP and DLNA support, that front-runners like XBMC and Boxee have to offer. However, these and many other more advanced features are planned for the future, so Enna still has a chance of rivalling the top players one day — just not quite yet. If you do use Enna, let's hear what makes it your media centre of choice in the comments.