There are two things can do to eliminate as much lag as possible.
1. Send your TV it's native resollution when possible. If you are using an Xbox360, set the output resolution to 1080p. If you are using a PS3, enable all resolutions and let the PS3 decide the optimal resolution.
2. Turn on Game Mode for your TV. It's either done through your picture menu settings or through the "Picture" Mode button on your remote.