My Garmin Edge 800. Cycling without it would be pointless as its only figures that keeps me going and also the virtual opponent in the Edge believes in political correctness and equality and it does not say "Keep up you fat b*****d" when I'm labouring up a steep hill, like real opponents.
But there again I wish it did as its proven that getting mad and aggressive helps your performance, so perhaps Garmin should bring out a software update to make it more aggressive and do away with all the beeps, and replace it with foul language and rude gestures.