I would suggest you spend time reading, at the very least, every wikipedia article on Kamen Rider and its movies, because you'll acquaint yourself not only with main riders, but secondary riders, evil riders, villains, important plot points, amd of course, movie riders like New Den-O (who you obviously haven't seen before, so watch Den-O Final Countdown!!!!)
Honestly, I only have 55 minutes, and 20 of that is on video clips I've put together. That gives me 25 minutes to talk about the history, so it is pretty much just a basic history to get people interested in the series if they haven't been before, and to entertain (since that is what a panel needs to do).
Hell, I had my panel supervisor last year so impressed with my History of Super Sentai panel that it made her want to check some of it out. She said that if they had told her it was related to Power Rangers when they assigned her to the panel, she would have turned it down.
Here is the current break down of my panel:
Show opening clips of Kougami wishing Kamen Rider a happy birthday along with the roll call from Let's Go All Kamen Riders, along with the roll call for Fourze and Wizard.
Talk about Godzilla, Ultraman, and Ishinomori.
Show clip from Skullman anime and Gilgamesh.
Talk about the creation behind Kamen Rider with Hiriyama, how the second rider came into being, and show clips from the very first episode (when Shocker transforms Hongo and his fight against the Spider Man in the gravel pit).
Talk about how the series progressed and show a clip of Black dueling Shadow Moon.
Discuss the break the series had in the 90s outside of Shin. ZO, J, and then show a clip from Kuuga (the church fight with No 3).
Talk about how Sentai has had some influences on the show due to the increasing number of riders of the years.
Show a clip from Saban's Masked Rider and Dragon Knight as I mention the two times Kamen Rider has been adapted for the US.
Show my trailer for my 2013 Sentai vs Kamen Rider panel.
