Right now if I type:
raspistill -t 60000
I can see the image on screen for 60 seconds, but I just want to show what the camera sees at all times. I am connected via HDMI.
You can just pipe raspivid straight to mplayer, rather than using nc to send it across the network:
raspivid -fps 20 -t 99999999 -o - | mplayer -fps 20 -cache 1024 -
You should be able to change fps to get a suitable frame rate, but both fps numbers should be the same to make the video output match the recording.