Well for the few things I do have on my PC, I use Windows Media Player's library sharing, and point it specifically at my video and music folders. Anything placed in those folders gets shared automatically and I can stream them from my Xbox 360, even if I never actually open WMP. Though some files won't play (unsupported codecs/file types). Using PS3 Media Server fixes compatibility issues, but has to be manually run on the PC, and I've only got one PC so I don't have dedicated hardware for it.
I guess I know how to get started on the storage and streaming of my own files, I'm more curious about streaming them off the net using whatever services I can get hooked up to my TV. I want something with a pretty comprehensive collection, that will allow me to buy movies, or just give me access to so many that I won't ever need to buy (I want to be able to think of a random movie, and watch it, not worrying about availability. I can (mostly) do that with Blu-ray, but I want digital). Since I will likely always have a gaming console, and those are supporting things like this more and more, I assume that is the route I would want to go. But, VUDU (Ultraviolet)? Amazon Instant Streaming? Something else? And if I start purchasing movies through one of these services, what's the chance it will be available on my new console? Just opening up the video app section on the Xbox 360, there are 54 apps... Most of which I don't even know what they are.
Netflix I've used. I'ts good for browsing and finding something to watch, but they usually don't have much that's new, and they cycle what they have all the time. Hulu+ is basically TV shows, but not many popular ones, always significantly delayed behind normal air dates, and half of them aren't available on TV connected devices (so PC browser only).
EDIT: I guess specifically, I'd like to know if anyone has experience, or has heard about experiences with some of these apps/services. Amazon/VUDU I've heard about a lot, and may be a safer bet. I don't know anything about any others.