The unrated version of 2010's Hot Tub Time Machine is available for free to rent (not own) on Xbox Video. The offer is available through this weekend only, for both the HD and SD versions of the film.
From EntertainmentForXbox on Twitter:
Hot Tub Time Machine 2 arrived in theaters this week, so if you want to see the first movie before watching the second, now would be the perfect time to do so.
Update: The offer appears to be US only at this time