A recent blog post by Bethesda, releases patch details for Skyrim v1.6, which include “Mounted Combat”. I know many people asked for this during Skyrim development and the fact that it’s being patched in for free gives everyone the opportunity to gallop around lopping heads off. You can currently beta test the patch now on Steam but be warned, it could break your save games or burn your house down, so unless you gotta try it before anyone else, probably best to just wait for the official release.