If you've got an android phone, how does Free sound?
If you use XBMC (xbmc.org) as your media player, they have a full-featured android app to control the software (from anywhere on your network).
Their app also integrates with android such that you can browse to a YouTube video, and it will ask if you want to play it with one of the apps on your phone (like the web browser or YouTube app), or if you'd like to stream it to your XBMC.
I've been using the stand-alone XBMC-Live linux distro on a set-top box for a couple years now and love it. I've got a regular Windows media center remote to use in the living-room, but use my phone to control it when I'm in another room and want to change songs, or stop the kids movie so they can hear me yell at them.
I'm sure there are a lot of other similar options, but since I use XBMC, that's the one I went looking for and use.