It's a real shame they decided to drop Front Row in Lion and ML, especially if you were using it to play iTunes medis on an iMac or laptop rather than a TV.
If you were connecting to a TV, then for iTunes purchased content you consider an AppleTV device.
I've held off updating my Mac Mini as i want Front Row on it, but to be honest rarely use it.
The problem with AppleTV is more limited format support.
In addition to Plex (which I have on the Mini and irritates me because I cannot stop it launching the server on startup), consider XBMC: