What's a good video resolution for the web?

I’m wondering what a good, or should I say user friendly, video resolution for the Web would be. I’m using a 640×480 resolution on my website but the screen just seems too large. Does anyone know which sizes Web masters generally use? Which resolutions can I go with to make the screen a tad smaller?

Also, say I record a video of my desktop (1366×768), and I want to reduce the video resolution to 640×480, or an even smaller resolution. What’s the best way to go about doing this without making the video look crappy or discombobulated?