aside from Netflix, Hulu, etc, there are plenty of other channels on Roku to check out. many of them consolidate various Internet video streams so you don't have to scour Youtube. for example, the Revision3 "channel" has Epic Meal Time, Digg podcasts, Ben Heck, and more.
the private channels are also interesting. "private" in this case means a developer is working on it and doesn't feel it is ready for mass consumption on the Roku channel market yet. they cater to all sorts of interests, from music to firearms to the Shamu Cameras at SeaWorld.
I only pay for Netflix, but I have a ton of smaller official and private channels added. I'm never bored with what's on (worse comes to worse, there are a ton of streaming music stations to listen to).