Here's a thread on this topic you'll find useful - http://members.founderdating.com/discuss/644
Also, in that thread you'll see I recommended Grumo Media. His PadMapper video is one of my favorites - http://grumomedia.com/new-grumo-what-is-padmapper/
If cost is an issue, though, the creator of Grumo created a course that teaches you how to craft your own demo video. It's like 10 hours of instruction and quite comprehensive (actually bought it myself). There's also one version of the course that leverages Adobe Illustrator & After Effects, and one version of the course that simply leverages Keynote.
Using the Adobe suite - http://grumomedia.com/how-to-create-an-awesome-demo-video/
Using Keynote - https://www.udemy.com/how-to-create-an-awesome-animation-in-keynote/
Hope any piece of that helps. Cheers!