Stargate: SG-1 should have ended at season 8. They beat Anubis, all the conflicts were tied up, there's a nice scene where the crew is just relaxing at O'Neill's pond. And then they ordered another season. So they did the same thing that Xena did and said "Well we ran out of ancient dead religion gods, I guess Christianity is next except they still exist so we have to be kinda cagey about it" and just kept making the show.
It was supposed to end there. Series 9/10 were meant to be a new show called SG - Command but Sci-Fi wanted to keep the recognised branding and show name so SG1 carried on. I think there was some good stuff in the Ori arc too.