I was annoyed when I saw that Apple killed support for FrontRow too. I'm not sure why they would do this, I liked to use it all of the time.
Plex and XBMC are certainly good alternatives and is probably what you'll want to use to replace FrontRow. (Plex would be my first choice:) )
Another suggestion might be to get an Apple TV to solve this issue. I'm assuming you used FrontRow while your computer was connected to a TV or monitor. An Apple TV has the same sort of interface as FrontRow and would surely play your iTunes Movies.
I kinda hope they bring it back in the future :/