While not a trusted source, wikipedia is stating that there will be three new Poirot films in 2007, and another three in 2008. This is extremely good news after the prospect the show had been cancelled. They state that this year we will get Dead Man's Folly (October), Mrs. McGinty's Dead (November) and Three Act Tragedy (November). While in 2008 it will be Appointment With Death (February), The Big Four (May) and the long-anticipated Murder On The Orient Express (September). This will leave just six Poirot novels left in the canon, as well as one short story and the whole Labours Of Hercules collection.
The link can be found here - just scroll to the bottom of the page.