I will sign up for VUDU just for the free movies -- if I can cancel after a trial
Vudu isn't a subscription service like Netflix, so there's nothing to cancel. It's great to rent movies from, though. You defiantely want to use that over Amazon as Amazon only streams in 720p.
One free app I can't live without is SkyNews, if you would like to use the Roku for something other than movies. Pandora is another good one.
I am curious as to your thought on a blu-ray title vs. an HDX title on Vudu. Perhaps you can use a UV code on a new release to facilitate a comparison?