Although there's already been a film based on the book, there hasn't been a Witcher film since the video games propelled the IP to international acclaim. That's going to change over the next year or so, with news out of the Polish Film Institute that Oscar nominated animator Tomasz Bagiński is working on an adaptation.
I'd love to see an animated version of The Witcher Saga. Perhaps done in the style of the Spawn series from the late 90's.