You could start with the usual suspects, CBS, ESPN etc. I think you will need to test with rule tracing to get the biggest hitters. We also squash a lot of this on the routers, by not giving this traffic priority, so it makes it painful for the user.
Here's a rule that denies access to the main NCAA.com streaming link and also denies requests that include a referer for NCAA streaming URLs. In testing it seems to deny access to the stream on NCAA.com, cbssports, tnt, tbs, and trutv.
If for some reason this ruleset doesn't work as expected, let us know what sites you are able to access the video on, what browser is being used and a rule trace if possible. Testing with IE, Chrome and Firefox has been blocking all of the videos for me.