listing nodes without redundancy

Hi every one,
I have a small question: How can we list distinct
nodes ( without redundancy)?
In the example below, i want for example to list
manufacturers (mercedes,peugeot,Renault)with no
redundancy.
Thanks
Taha. 

<cars>
	<car manufacturer="mercedes" model="240"/>
	<car manufacturer="peugeot" model="206"/>
	<car manufacturer="peugeot" model="405"/>
	<car manufacturer="mercedes" model="240"/>
	<car manufacturer="Renault" model="clio"/>
</cars>

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