For those interested in live streaming/recording A/V:
Audio Hijack Pro: Excellent and simple piece of software that can take control of individual or all audio sources. You can add effects, voiceover, and my personal favorite, use it as a mixer in order to change and monitor audio levels. To top it off, it's only $32, and the free trial is fully functional. It just adds some extra noise for sessions longer than 10 minutes.
CamTwist: A virtual camera that can capture and route video from various sources, including your desktop. You can overlay various special effects to your video, maintain different sources and combine them for a real studio-like presentation. The best part is that it's compatible with many other pieces of software that receive video input. My favorite feature is the option to "confine" your desktop capture to a specific application, meaning you can move Spaces or other windows over the selected region and they won't be captured. Did I mention it's free? No? Well, it's free.
Wirecast: Professional streaming software. It's pretty expensive, but very easy to use and has a ton of features. Considered one of the best in the market. Works great with CamTwist.
Flash Media Live Encoder: A free alternative for streaming. Not as featured as Wirecast, but it can do basic things just fine. Also works with CamTwist.