Gamertell has posted a list of 16 movies recently and soon-to-be released on UMDs for the PSP.
From the article:
"So maybe the UMD movie format didn't work out as well as Sony may have hoped. A lot of stores have given up selling movies on UMD or at least cut back its numbers considerably but, believe it or not, there are still new UMD movies on the horizon for PSP. Most if not all of the new and unreleased UMD movies are made by Sony Pictures thus making the selections pretty limited."
Note that the UMDs listed in the article have been or are being released September 2008 through January 2009.