The Ubuntu Artwork group on flickr shortlisted 20 wallpapers to be featured in Ubuntu 10.10 out of a whooping 5,345 submssions. Have a look, download and set one of them as dektop background now.
Don't forget to toggle full screen.
Edit: On the flickr group there are 20 wallpapers but in official tarball there are only 17. So there will be only 17. Download them from here.
Lastly, Canonical Design Team revealed the new radiance theme for Maverick.