I have several, but whenever someone mentions guilty pleasures, Event Horizon is one of the first ones that pop into my head. While no masterpiece the film is incredibly well shot and made an impression on me when I was younger. And it's a lot of fun in a certain kind of way.
Event horizon is so good. Very few other films combine sci fi and horror so well.
If we’re defining guilty pleasures as “no masterpiece but I could watch them any time, any reason”:
Groundhog Day
Short circuit
Final destination series
The village
Signs
Resident evil 1
The burbs
Predator 1/2
Constantine
Face/Off
The goonies
Sideways
Equilibrium
Revenge of the Sith