More recently, they've cancelled Eureka. That was a bummer because that also was one of my favourites.
To the OP, I think Fringe had slowly run its course. It was one of my favourite shows, but after a while it just began to feel like the X-Files - very little forward momentum in story, throwing up more questions than answers, that kind of thing.
The Adventures of Merlin was also cancelled after 5 seasons just last year, but I think they did the right thing with that one and ended the series properly, with an actual end rather than a Cliffhanger.