recent TechCrunch article mentioned a new search engine called CanIStream.it, which lets you search for movies to see whether they are available on the web. It searches the usual suspects (Hulu, Netflix, Amazone, iTunes, etc.) and even gives links to the iMDB and Rotten Tomatoes pages where applicable. Even if your movie isn't streamable, you can still find links to rent or purchase copies, and if you're interested in the Blu-Ray version, there might be an Amazon link to purchase a disc.
Sign up to receive a notification if/when your movie becomes streamable. And there's a free app in the Apple store.
CanIStream.it doesn't do TV shows, so you might still need Clicker.com for those.