Ask HN: How can I make a good screencast?

I'm thinking of making a video screen cast (as opposed to a written tutorial) to show off my SDK and embedding it on the front page of my site. But I'm pretty clueless of the tools out there for OS X. What are the good ones to use?

Any tips as well? I'm thinking I'll record myself using the SDK, then adding my voice on top in a second recorded track. I would like the video to be 5-10 minutes, or just enough to show the developers (my target) what makes my SDK useful and productive. But this is just a complete guess at what defines "a good screencast".

Lastly, my voice is not the greatest to listen to. If there are any audio recording/editing technique to make it sound better please let me know.