If you fancy extending your authoring skills over the holiday, check out Yacapaca’s list of permitted embeds, which I have just updated.
Author Kevin O’Driscoll has produced some great exemplar material combining video with quizzes. Try his course AIMS practice: Strand 1: Number Sense to get an idea of what is possible.
If you already have a lot of PowerPoints that you want to share, take a look at SlideSix (update 2013: SlideSix appears to be defunct. Very sad). Whilst lots of services will allow you to upload PowerPoints, they are usually not much use without you there to narrate them. SlideSix allows you to add the narration too, so you can quickly convert your live presentations to video and link them to quizzes or courses.