Gunshow, Dinosaur Comics, Chainsawsuit, Diesel Sweeties, Girls With Slingshots, Saturday Morning Breakfast Cereal, Perry Bible Fellowship...
Definitely Dinosaur Comics is one of those examples that really exemplifies old webcomics the best. It's a strip that's extremely nerdy, focused on one gimmick stretched to the absolute limit, and it somehow launched the creator to becoming a prominent ad company man then later one of the top writers in traditional comics as well.
I also think Gunshow's Anime Club is one of the best pieces of media to represent the late 00s/early 10s era internet culture. It's nothing at all that could be famous if you published it in 2021 but back in the day it really worked, I think.