Gary Larson's one-panel comic The Far Side spawned quite a few one-panel gag comics without recurring cast members, such as Close to Home, Real Life Adventures and The Argyle Sweater. Mother Goose And Grimm sometimes engages in Far Side-style humor as well.
For the first Garfield compilation, Jim Davis came up with a new long-page book design to accomodate the three-panel strip most legibly. Once the "Garfield format" of books became popular, many other comic strip trade books began using it as well, including Fox Trot and the aforementioned Far Side. (Ironically, Garfield itself no longer does.)
Interestingly, Marvin seems to have aped a lot of the stylistic traits from early Garfield.
Incidentally, Garfield himself is this, debuting five years after another orange fat cat, Heathcliff.
Doonesbury was one of the first comic strips to use a One-Two Punchline, now seen in countless comics. It's also the Trope Maker for pretty much every strip that even so much as dabbles in political/topical humor.
And if Doonesbury didn't do it first, chances are the more off-the-wall Bloom County did. Interestingly, Berke Breathed admits that he cribbed Doonesbury a lot in the early years.
