I know this is a pretty popular one but I don't think I've ever not felt better after an episode or two (or 6) of Futurama. As for movies, Hot Fuzz always has something new and funny you hadn't noticed before on each watch.
I also think many of the studio Ghibli films give off some pretty good vibes (emphasis on the word 'many' though, there are some pretty gut-wrenching ones). Any of the Mr Bean movies or episodes also cheer me up pretty well. ETA: for shows that leave you feeling positive, many of the Star Trek series focus on the good aspects of humanity, and present very meaningful ideas on how to achieve a positive outcome for all. My personal favorites so far are Deep Space 9 and the Next Generation, although Voyager and many of the others are just as good.