Through my career, I have delivered over 100 invited talks around the country and around the world. This page includes abstracts and the slide presentations for most of these talks. Many of the talks evolved over several presentations—the slides here are the most recent.
You can clearly see the evolution of the quality of presentation materials in this content. For many years, presentations were handwritten on vugraphs or even chalktalks because including mathematical equations and figures was just too difficult. In some settings, spontaneity was encouraged—at early Dagstuhl seminars, for example, people were encouraged to not make their slides until the night before the talk! So, you can expect to find plenty of bugs in the early talks.
Why not post videos of the talks? This will likely be the norm in the future, as people gain experience with the video production workflow, but my feeling is that videos taken from the back of the room, as has been typical, are rarely worthwhile.
Some of the information in these talks is also found in research papers or books, but much of the content is uniquely present in the slides. While these are hardly authoritative sources, many people have expressed interest in this content.