Super Mario Bros.
Yes, this movie is cheesy, and yes, it completely butchered the games, but, still, it's a fun action-adventure romp with a pretty great cast.
Willow
I will forever regard George Lucas as a creative mastermind, and Willow is one of the prime examples of why. You've got Warwick Davis in a starring role as the archetypical loveable underdog hero, Val Kilmer as a long-haired barbarian swordsman with a sarcastic wit to rival that of Princess Leia's, and an evil queen who'll give your kids nightmares. What's not to like?
Mars Attacks
Myself and a small group of friends - most of whom I've now lost touch with, sadly - seem to be the only people who find this film even remotely funny. My favorite part is actually the ending, since it's so blatantly over-the-top that you can't help but laugh. Tim Burton definitely knows how to spoof a genre while at the same time creating a genre of his own, and MA's the quintessential example.
Men in Black
I'm a huge fan of both these movies, atlhough I haven't watched them in years (mainly because I have no idea where they went). MiB did something similar to Mars Attacks in that it put a spoofy spin on the alien invasion movie genre, but simultaneously took itself and the universe it was depicting seriously.
Serenity
I'm listing this here because, to this day, I'm one of the few people that I know who's actually seen the film (or the TV series Firefly), so it definitely qualifies - at least for me - as a guilty pleasure, something I can watch over and over without caring what other people think. It's been said many times, but Joss Whedon is a genius, and Serenity proves that. It's got everything that made Firefly great while it lasted, only ramped up 150%.
Masters of the Universe
As a HUGE He-Man fan growing up, this remains a very nostalgic film for me, especially because of the fact that, changes and all, it has as its source material what could be considered a lost art form: a true Saturday morning cartoon (and a great one to at that). Dolph Lungdren is probably the only person - at the time or now - who could have played the character of He-Man, and he does it remarkably well, and Frank Langella is the PERFECT Skeletor; you've also got a young Robert Duncan McNeill, a young Courtney Cox, and Billy Barty as one of the funniest comic-relief characters I think I've ever seen in an action film.
Mighty Morphin Power Rangers: The Movie
I've never been afraid to admit my love for the Power Rangers franchise (even at 28 years of age now), and MMPR:TM has a special place in my Ranger-loving heart, most particularly because it gave us one of the funniest villains I think I've ever seen ANYWHERE in Paul Freeman's Ivan Ooze. Despite the fact that the film exists outside of the Power Rangers canon, it still holds a pretty significant place in the mythos of the franchise, and is a pretty fun film in its own right.