Ehhm, i wouldn't say the "what's in the box?" part of Se7en is a twist really. More just a shock moment, but the film revelled in shock moments anyway. It's more the fact that the serial killer had planned for emotional reactions to complete his "work" that brought the jigsaw together.
Anyhow, has anybody seen Lucky number Sleven? Not perfect by any means, but some interesting play in there. And starring M. Freeman! (As a bad guy nonetheless)
There's also an interesting film called The Disappearance of Alice Creed that is sort of like if someone decided to make a story comprised solely of plot twists. Fascinating to watch unfold and must take a fair bit of skill to pull off that effectively. Recommended if only to try and figure out whether it requires its' own genre. And if so; where to find more, as it's pretty damn entertaining!