Where can I download free wallpaper ?

Try These..i dont like elementary but...

http://elementaryos.org/journal/luna-wallpapers-officially-revealed

http://www.clearbits.net/

Searching for 'wallpaper' has a few collections.

and

CC images from flickr

http://flickrcc.bluemountains.net/flickrCC/index.php?terms=wallpaper&page=1

Also, searching for generic terms like 'nature' , 'beach' or 'desktop' will show a few suitable ones.

extra: I keep these on an online bookmark site for easy personal reference (and for anyone into free culture content), at http://perthfreeculture.org/

This incantation might help you dig some cc by and by-sa files from flickr.

http://flickrhivemind.net/flickr_hvmnd.cgi?search_domain=Text&textinput=wallpaper+desktop+background+-seamless+-tile&search_type=Search+Text&photo_number=100&photo_type=250...

Thanks for your help ;)