If you need id as the key, then rely on the Collection:

$collection = Model::all();

$collection->getDictionary();

// returns:
array(
  1 => object(Model) ( ... ),
  2 => object(Model) ( ... ),
  ...
  idN => object(Model) ( ... )
);

Otherwise, nice or not, you can do this:

$keys = $collection->lists('columnName');

$arrayOfModels = array_combine($keys, $collection->getDictionary);

I'm not sure the code below was there when this thread was opened, but there's a clean way to do it now:

$collection = Model::all();
$rekeyedCollection = $collection->keyBy('some_attribute');

And in my use case I wanted a unique set of Models so I then used:

$set = $rekeyedCollection = $rekeyedCollection->unique();

Hope that helps :)