Ancestry.com has recently added a collection called "Missouri Marriages 1805-2002." Frequently, Ancestry's state collections have seemed to promise more than they deliver--being limited to just a few counties or even a few years though the title implies many more counties or years.
But this collection seems to be the real deal. Easily searchable, it has many, many, actual images. And it seems to include the excellent collection of marriage records from Jackson County. Indeed, I found one record on this site that's not in the Jackson County collection. So, kudos to Ancestry for this outstanding addition!