I've always loved the Pink Panther films. But I will be a bit controversial here and say that I actually prefer some of the later films... This is still an absolute classic though, and should be watched at the earliest opportunity.
I first saw this when I was about 10 and it's been part of my life ever since I was a kid. The Pink Panther films just stay with you. They are also immensely quotable!
Peter Sellers steals the show. Intended as a film for David Niven, apparently Sellers' improvisations were so good that Edwards started to steer the film in the bumbling detective's direction. It's clear when you watch the movie that Niven couldn't hold a candle to Sellers. For good reason!