If you have a fancy HD television and a box with a HDMI port, it’s (kinda) easy to setup your TV as a secondary monitor at full resolution, with audio support. Needless to say, it’s great for watch all those HD movies in a big TV instead of staring at your monitor or a small netbook screen 
First, the video. Run xrandr and see which devices you have available. My Acer AS1410-8414 running Arch Linux gives this output:
Screen 0: minimum 320 x 200, current 3286 x 1080, maximum 8192 x 8192
VGA1 disconnected (normal left inverted right x axis y axis)
LVDS1 connected 1366x768+0+0 (normal left inverted right x axis y axis) 256mm x 144mm
1366x768 60.0*+
1024x768 85.0 75.0 70.1 60.0
832x624 74.6
800x600 85.1 72.2 75.0 60.3 56.2
640x480 85.0 72.8 75.0 59.9
720x400 85.0
640x400 85.1
640x350 85.1
HDMI1 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 698mm x 392mm
1920x1080 50.0*+ 60.0
1280x720 60.0 50.0
720x576 50.0
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)
TV1 disconnected (normal left inverted right x axis y axis)
The GPU is a Intel GMA 4500MHD, by the way. LVDS1 is the default LCD screen and HDMI1 the port I’m using. So, to maintain your current screen and create a new one in the TV, run:
xrandr --output HDMI1 --auto --output LVDS1 --auto --left-of HDMI1
This will output a screen on the TV with automatic resoution (1920×1080, in my case), and also keep the current one in the laptop screen at the left side of the TV. Different GPUs have different ways of doing the same thing – in a laptop with a Quadro NVS 140M I was able to use nvidia-settings to configure a second monitor, even having the option of a unified desktop using TwinView (the same effect attained here) or two separate X screens. I suspect ATI-based GPUs have a fancy GUI program as well.
In a next post I’ll explain how to easily redirect the audio to the HDMI port using PulseAudio, if your system insists on outputting sound through your computer speakers. In this case, you could just use a cable with a 3.5mm plug in each end, but why waste plastic and metal when your powerful HDMI cable can transport sound too?
P.S.: I tried to watch a sample from the Apple QuickTime HD Gallery , but my netbook’s Core2 Solo 1.4GHz just doesn’t have what it takes to watch 1080p in all its glory. Meh 