Here you can find levels submitted by other registered users of X Ball. To play on the levels you download from this site, place them in the "Worlds" folder inside of your "X Ball" folder and then chose "Change The World" from the X Ball main menu screen. For more detailed instructions, please see this page.
If you feel inclined to create levels of your own, I would be more than happy to post them here for other users to enjoy. You can submit your worlds by filling out this form.