so check this out, the new sony mylo uses the same 320x240 wallpaper resolution right? since more indie kids/teens are probably going to get a mylo before a blackberry, chances are more sites with wallpaper are going to gear towards that group.
so, i did a search for "mylo wallpaper" and i got about 5 hits back. this site, sonymylowallpaper.com
has quite a few decent ones.
so start searching and post your finds!