If you are in North America, Insteon will work nicely for you.
you don't need the whole ELK M1 Gold...unless you want to integrate that too
Insteon Integration via a PLM is in public RC1 testing (yes, it works very well)
Make sure you get a PLM 2414S (that's the Power Line Modem) that is the device you connect up to linuxMCE.
Insteon has a wide range of dimmers, depending on what features you want. Timed dimmers, KeypadLincs (which have up to 8 buttons for other devices), SwitchLincs, etc.