Hmmm. I really don't do the "guilty" thing. If I like it, I like it. I'd say the closest thing to a guilty pleasure would be all the bad horror movies my wife and I watch. It's all in fun, though. We KNOW they're bad.
I still have a soft spot for 80's fantasy movies like The Dark Crystal, Legend, Labyrinth, Willow, The Never Ending Story, etc. That's pretty much pure nostalgia, and I am not guilty in the least.
Heck, I still unreservedly love the Transformers Movie. It's a heck of a lot better than anything Bay has put out.
I can't think of any more recent movie that would count. Maybe Priest? It was pretty crappy, but I still kinda liked it. Or the goofy ass Crank movie with Jason Statham. Totally nuts.