To inaugurate a 4-part series on "Television's place at the center of our culture" in The Globe and Mail (Canada's national newspaper), tv critic John Doyle gives a "personal selection of the medium's historical highlights".
Here is this list of "Television milestones", from The Globe and Mail, Sat. May 26 2001, p. R1-R2. I edited out the little comment for each, quoting only the one about Seinfeld.
May, 1939: RCA broadcasts the first live sports event on TV.
Fall, 1951: I Love Lucy.
March, 1954: Edward R. Murrow investigates Senator Joseph McCarthy.
Fall, 1960: The Nixon-Kennedy election debate.
Fall, 1966: W-Five is launched [Canadian current affairs magazine].
July, 1969: Man walks on the moon.
November, 1969: Sesame Street.
Fall, 1971: All in the Family.
September. 1972: The Paul Henderson goal. [IIRC, during the Canada-USSR hockey series.]
Fall, 1973: Upstairs, Downstairs on PBS.
June, 1985: Live Aid.
"Summer, 1990: Seinfeld debuts. A seemingly slight show about a comic and his single pals (NBC famously ordered only four episodes). Seinfeld eventually transformed the sitcom, setting a standard for wit and originality that was never matched during its long run."
Fall, 1990: Twin Peaks.
Fall, 1996: The Newsroom [Canadian satire about the news department of the CBC station in Toronto.]