Most Pivotal SG Moments (possible spoilers)

[Pharaoh Atem]

Expedition to Atlantis
Meeting the Asgard
Daniel figuring out the point of origin and finding the gate address on Abydos

[Qtyled]

We should make a poll.... but what to put in it?!

Daniel figuring out the point of origin and finding the gate address on Abydos

That's probably the most influential.

[wurlitzer153]

How about the entire fifth act of Reckoning II (and maybe a little of the fourth, can't remember where the commercials were). That, to me, is the climax of the entire series, not counting the Ori stuff.