Snakes on a Plane, or SoaP, is awesome. I laughed almost all the way through it - so long as you realise it's not meant to be a serious action film (I hope!) then it's a good bet.
A Scanner Darkly looks awesome but since it's only showing at a handful of cinemas across the UK you might not be able to get to see it like me

DONT go and see the new Jack Black film. Although I haven't seen it myself my bro saw it and said it was shite. Not that I expected it to be good anyway.