CSS transition to/from 'auto' for top, left, width, and height properties.
I basically took the code by Nikita Vasilyev's CSS transition from/to auto values and turned it into a plugin.
Options are property (either 'top', 'left', 'width', or 'height'), value (defaults to 'auto'), transition_affix (default transition asides from transition-property, defaults to ' .5s ease-in-out').
E.g.
$('#element').autoTransition({ property: 'top', value: '200px', transition_affix: ' .2s ease-out', callback: function(){ } });