YouTube Salar Kamangar confirms that starting today it will add around 3,000 new movie titles for rental in the US, along with reviews and behind the scenes extras.
Update: Additional details have been posted on the YouTube Blog and are also after the break -- NBC Universal, Sony Pictures and Warner Bros. are the new studios YouTube is partnering with to add the 3,000 new and catalog releases, doubling the amount previously available. The pricing is $2.99/$3.99 for movies viewable via PC or Google TV (no other device support is mentioned) and the FAQ notes that YouTube supports resolutions up to 4K but "most" of the new additions are sadly in SD, a choice which is apparently up to its partners.
Update 2: The YouTube Movies page is updated now, as seen above. There's plenty of well known movies to be seen now replacing the catalog of older and indie movies that filled the page before. Rotten Tomatoes ratings integration is also front and center, while the Extras are on each movies individual page, but really just show a list of related videos on YouTube, while there doesn't appear to be a way to tell if a movies is one of the few in HD before you pay.