Can you recommend a free and fast screen sharing application?

I occasionally enjoy watching long videos online with distant friends.

I find they struggle to get to the content, wherever it is, and we spend hours debugging their machine before we can both relax and simultaneously watch a show and chat.

I have decided it may be easier just to get it working for me and invite them to share my screen. I know that there are applications available, but are any fast enough to give them good image quality? Do they also transmit audio?