It should stand on its own, not simply reproduce what your company or organization already has created for print or other media. This doesn't mean you have to start completely from scratch, however. Usually this can be accomplished through writing and editing. However, don't overdo it with links, or a too-complex navigation structure.
Images can be content, too.
Consider adding photographs or illustrations that may have been excluded from printed materials due to space considerations or printing costs. Be sure only to add images that communicate something the reader would find significant, however. Images take much longer to download than text, so the pictures must be worth the wait. Consider whether animation, video, or sound might offer significant value to the user. Such exotic types of content can be fraught with pitfalls, however.