I've just finished reading David Copperfield (as recommended by many of you) and Barkis' proposal to Pegotty 'Barkis is willing' made me roar with laughter
My all time favourite literary proposal is Gabriel Oak to Bathsheba Everdene which ends with the words
'...at home by the fire, whenever you look up, there I shall be -- and whenever I look up there will be you.'
Can you think of any other fantastic proposals?