TwonkyMedia Manager is not just another iTunes knockoff. It's a full-fledged DLNA (Digital Living Network Association) UPnP client/server that allows you to play any media found on PCs or DLNA devices (TVs, game consoles, A/V systems, digital media adapters and mobile devices, game consoles, etc.) on your network, as well as local media found on your PC. Most non-DLNA certified UPnP devices will work as well, and TwonkyMedia ($40, 30-day free trial) can also access media from Flickr and YouTube after you provide your online username for these services. Internet Radio streaming is offered as well.
TwonkyMedia Manager handles music, images, and video and is nearly an industry standard--it's the embedded media server on a number of network attached storage boxes. The program is easy to use, though the help file dwelled unnecessarily on why the program is so great and what you can do with it. I wanted to find out how to add media to the program, and it took more digging than I'd like to find out that you must add a path to it on the server settings page in the configuration dialog. You can't simply click an add button on the main page or drag and drop files or folders to the TwonkyMedia Manager interface--a usability issue I'd like to see addressed.
Other than those minor nits, I really enjoyed the time I spent with TwonkyMedia Manager--it streamed media to other PCs as wells as from my Synology NAS box and everything else I tried it with flawlessly (HD video performance is subject to the speed of your network). The interface is easy to look at and if your media sharing needs extend beyond sharing iTunes music libraries, it's well worth a look.