Although I liked the fifth season of The Venture Brothers, the fourth season finale actually felt like the show was over. The boys graduate. Gary has it out with the Monarch. Hunter gains control of SHIELD. Sgt Hatred gets back Princess Tiny Feet. Brock gets the final brush off from Mol and returns to the Ventures.
Yeah, it was not a cliffhanger per se. However, it really would have been a perfect finale. If anything, I worry they'll not be able to top it with the actual finale.
In another "it wasn't necessarily a cliffhanger" example, the Fifth Season finale, where the FBI raids a mob sit-down and Tony has to run back home through the snow, into Carmella's arms, could have functioned as a finale if need be