Farscape - 4 seasons
Sliders - 5 seasons (2 on SciFi)
Stargate SG-1 - 5 seasons (on SciFi)
Battlestar Galactica - 4 seasons
Stargate Atlantis - 5 seasons
I'm seeing a pattern here. Sliders is a bit of an exception to the SciFi rule, as it had a whole saga of a behind-the-scenes issues, but the others were all highly successful (for SciFi) at the time they were cancelled. Eureka will probably be cancelled after the fourth season at this rate, and then what will SciFi have? Nothing. And good riddance to them.
ETA: Wait, MGM pulled the plug? Oy. Even better.