This is a list of spam floods on /b/ that I came across in the /b/ archive.
Xena fanfiction - Around April 9 2006. Earliest flood avaliable in the archive. Sometimes in the middle of random threads someone will just begin posting excerpts of a heavily misspelled Xena fanfiction that can found here. It was also posted with a currently unknown image. In this thread here it happened about 10 times. Certified as a spam flood when I found a thread that was just a single copy and paste of the fanfic.
Furcism is as bad as Racism - Around April 9 2006. A copypasta of a furry who claims Furcism is as bad as Racism. The text of the pasta is avaliable here (at the top), and was known to be posted with a picture of Ghandi. Occured not long after the Xena flood. Dozens threads were made with just that copypasta, much larger than the other floods of the time, and Anti-Furry copypasta also began being flooded on a lesser scale (at the later points of the flood someone started flooding the flood threads with literal gibberish by slamming their keyboard). It was referenced in another thread here with the text "Too bad the thread was aimed at ALL furries, not just the guy who's spam-flooding /b/ with that fucking picture."