Never seen Firefly (don't think it was ever broadcasted here). Maybe I'll go watch it today.
I miss: Chuck, X-Files, Warehouse 13 and a few others. Unfortunately, each of those got worse near the end, which means that there's no good reason to let it continue. Of course Warehouse 13 could be restarted in the new warehouse, but to have a new crew for X-Files might not be the same (not to mention that they'd have to look hard to find mysteries nog covered by X-Files, Supernatural, Warehouse 13, and dozens of other series that spawned since the original X-Files was made). Chuck can't continue since it's not the same funny Chuck since he got happily married, became a real spy, and lost the nerdy mistakes. Can't let Morgan take over again either, nor just anyone else, as it would mean Chuck would have to lose the intersect or die (otherwise they can have him as intersect instead), and even if he loses it he can train the new one (again, unless he's dead).
I'd even not mind to see what was being planned for a second season of SGU, eventhough season 1 was one big soap. They were trying to recover from that a bit near the end of the season. But it wouldn't be my favorite to return.
I could go for the Dutch version of 'Whose line is it anyway?', but unless it would be the right people doing it it would not be nice either. They had too many people who couldn't do it near the end.
Maybe I'd have to go for Buffy instead. Always liked that series, even the last season.
Edit: On that list of 180 shows it has Sliders ranked above Chuck. I'd disagree with that. Eventhough it would be hard to bring Chuck back as a decent series after the end of the last season, with Sliders it would be even harder. The last season only had one of the original crew left, and he managed to get home. The rest were dead or lost on the way iirc. You can't just have a new group pick up where it left off, so it would basically be a remake. A pity, as the series was great.
Heroes and The 4400 are also on that list, and are ones I liked. Dark Angel was nice because of Jessica Alba, but the stories weren't always great. Would have expected to see Witchblade on that list too. ST: TNG I do miss somewhat, as well as ST: Voyager, but another season would have probably not done justice to either of them.