Not sure if it has been posted but I could not find the same information in the same area.
Take a look at
http://www.interfacelift.com, they have many wallpapers and categories to choose from.
Since most are not in the G1 format (640x480 pixels), copy the link of your desired wallpaper and head on over to
http://www.drpic.com Upload your image via link and then resize.
Very quick, and easy to produce the wallpaper your looking for. You could then upload your formatted image to the wallpaper section here for others to enjoy.
Dr Pic works for all types of images, web based or on your hard drive.