9. Firefly Season 2
Joss Whedon's superb sci-fi series Firefly was cancelled after a mere 14 episodes by the TV devils that are Fox - notorious for their terrible creative decisions - yet as a testament to the power of the Browncoats, we did actually get a movie spin-off, in Serenity. Despite fanboys like myself going to see the film multiple times (I saw it thrice at the cinema, and dragged all my friends along once), the film just grossed short of its budget, meaning a sequel, or better yet, another series, was never, ever going to happen. All we got was a few nice comic books that bridged the gap between where the TV series ended and the film started. My impeccable research indicates that an episode of Firefly costs between $800k and $2m depending on the set-pieces involved, meaning that even at the most expensive end, we could get about 6 episodes made for £10m, and given that this could be basically half a series, it's likely that a studio would commit to putting up the other half.