I might be wrong, but I'm sure I rememeber reading SG-1 had an original 2 season order.
From what I remember of the time was that after about 8 episodes in the first season it had 88 episode order (22 from season 1 and three more after that). I remember being surprised because that's rare in TV. But I can be wrong, I was 12ish at the time.
Then by the time they started filming the forth season they knew they had a 5th season. The 5th, 6th, 7th, 8th (And an 11th season) seasons were all planned as the finale season.