Arrested Development is coming back though. A 10+ episode season exclusive to Netflix, followed by a movie. It did have somewhat of an ending, as it became clear that it wouldn't survive past the 3rd season. The 3rd season was written to move toward some semblance of an ending, but with a clear ability to leave it open for a 4th season, since at the time it was hoped that another network (Showtime or HBO) would pick up the series.
Firefly would have to be the #1 answer for me, though. Fox never gave that show a chance. I think it shows how important that show was to people that it has such a large and rabid fanbase to this day, that it's inspired video games and comic books. They work Firefly references into Nathan Fillion's current show Castle to this day.
I felt Flash Forward and The Event were trying way too hard to be mysterious and capture Lost's audience. I never even got very far into The Event, because the mysteries were so spoon fed to the viewer that it wasn't really exciting to me. Flash Forward suffered from this early on, but anyone that toughed it out knows just how damn good that show got in the back end of it's only season. I think it started to have potential, but again they knew that they weren't going to survive for a season 2 and wrote the last episodes in a way that wrapped things up somewhat.
Also the Battlestar Galactica prequel spin-off series Caprica. Another show whose network never gave them a real chance. SyFy is about to do it again with Battlestar Galactica: Blood & Chrome, another prequel series that SyFy has so little confidence in that they may only broadcast it as a web series. You'd think they'd have a bit more faith in spin-off shows based on their most popular original series ever.
