You tube would be awesome! iPod does it, why not Zune?
I am not a member of Netflix, but everyone I talk to that is is very pleased with it. I would consider signing up if there was a Netflix app for Zune HD.
I would also love the ability to just watch movies online. There are so many sites (hulu being one, but not the only one) where you can watch TV shows for free. I would love to have this in a handheld Wi-Fi enabled device.