4chan: The Animated Series - First introductions:

Season 1, Episode 1 (Oct. 4, 2003) - /b/, /h/
Season 1, Episode 2 (Oct. 11, 2003) - /c/, /d/, /h/, /s/, /w/, /y/
Season 1, Episode 7 (Nov. 15, 2003) - /a/, /l/, /r/ (Trains)
Season 1, Episode 12 (Dec. 20, 2003) - /t/
Season 1, Episode 15 (Jan. 10, 2004) - /l/ (again), /r/ (now likes Requests)
Season 1, Episode 21 (Feb. 21, 2004) - /t/ (again), /f/
Season 1, Episode 23 (Mar. 6, 2004) - /q/
Season 1, Episode 47 (Aug. 21, 2004) - /m/, /n/ (now likes Trains), /cm/
Season 1, Episode 50 (Sep. 11, 2004) - /k/, /o/, /sm/
Season 2, Episode 3 (Oct. 16, 2004) - /ib/, /ip/, /v/, /z/
Season 2, Episode 17 (Jan. 22, 2005) - /e/, /3/, /g/ (now likes Technology), /n/ (now likes Nature & Wildlife)
Season 2, Episode 18 (Jan. 29, 2005) - /ic/, /p/, /x/ (General Photo)
Season 2, Episode 23 (Mar. 5, 2005) - /gif/, /hr/, /wg/
Season 2, Episode 27 (Apr. 2, 2005) - /fur/
Season 3, Episode 28 (Apr. 8, 2006) - /co/, /po/, /sp/
Season 3, Episode 29 (Apr. 15, 2006) - /cgl/, /ck/, /mu/, /n/ (News, old /n/ becames /an/drew), /tv/
Season 3, Episode 45 (Aug. 5, 2006) - /con/
Season 4, Episode 20 (Feb. 17, 2007) - /tg/, /x/ (Paranormal)
Season 4, Episode 49 (Sep. 8, 2007) - /rs/
Season 5, Episode 21 (Feb. 23, 2008) - /fa/, /fit/, /hc/, /n/ (Transportation), /sp/ (return), /toy/, /trv/, /jp/, /r9k/
Season 5, Episode 41 (Jul. 12, 2008) - /i/
Season 7, Episode 18 (Jan. 30, 2010) - /adv/, /lit/, /new/, /int/, /sci/, /3/ (return)
Season 7, Episode 42 (Jul. 17, 2010) - /vp/
Season 8, Episode 17 (Jan. 22, 2011) - /soc/ (earliest example of board existing)
Season 9, Episode 7 (Nov. 12, 2011) - /r9k/, /pol/, /hc/ (all returns), /diy/
Season 9, Episode 20 (Feb. 11, 2012) - /vg/
Season 9, Episode 21 (Feb. 18, 2012) - /mlp/
Season 9, Episode 22 (Feb. 25, 2012) - /hm/
Season 9, Episode 37 (Jun. 9, 2012) - /wsg/
Season 9, Episode 46 (Aug. 11, 2012) - /q/ (return)
Season 10, Episode 25 (Mar. 23, 2013) - /asp/, /gd/, /out/, /lgbt/, /vr/
Season 10, Episode 27 (Apr. 6, 2013) - [s4s]
Season 11, Episode 1 (Oct. 5, 2013) - /con/ (return)
Season 11, Episode 20 (Feb. 15, 2014) - /biz/
Season 12, Episode 17 (Jan. 22, 2015) - /qa/
Season 13, Episode 1 (Oct. 3, 2015) - /aco/
Season 13, Episode 6 (Nov. 7, 2015) - /his/
Season 13, Episode 7 (Nov. 14, 2015) - /trash/
Season 13, Episode 8 (Nov. 21, 2015) - /news/
Season 13, Episode 13 (Dec. 26, 2015) - /wsr/
Season 13, Episode 31 (Apr. 30, 2016) - /film/, /qst/
Season 14, Episode 2 (Oct. 8, 2016) - /vip/

Leaving:
Season 1, Episode 9 (Nov. 29, 2003) - /r/ (Trains)
Season 1, Episode 14 (Jan. 3, 2004) - /l/
Season 1, Episode 18 (Jan. 31, 2004) - /t/
Season 1, Episode 27 (Apr. 3, 2004) - /g/ (Guro) leaves for, like, one minute and decides to come back. Also, /q/ (no clear indication, say it happened here)
Season 2, Episode 3 (Oct. 16, 2004) - /n/ (Trains)
Season 2, Episode 6 (Nov. 6, 2004) - /l/, /sm/, /z/ (remains as a beehive on the tree outside for many years)
Season 2, Episode 8 (Nov. 20, 2004) - /g/ (Guro), this time for good.
Season 2, Episode 23 (Mar. 5, 2005) - /x/ (General Photo)
Season 2, Episode 28 (Apr. 9, 2005) - /fur/ (two-parter where /fur/ comes, terrorizes 4chan, then his room is nuked in the next part)
Season 3, Episode 15 (Jan. 7, 2006) - /5/ (gets dragged out of the house, only appearance. /b/ is like "Who was that guy?")
Season 3, Episode 45 (Aug. 5, 2006) - /con/ (one episode clip show)
Season 4, Episode 15 (Jan. 13, 2007) - /sp/
Season 5, Episode 21 (Feb. 23, 2008) - /n/ (News), /3/ (no clear indication as to when /3/ left, say it happened here)
Season 5, Episode 41 (Jul. 12, 2008) - /ib/, /ip/ (succeeded by their daughter, /i/)
Season 7, Episode 42 (Jul. 17, 2010) - /hc/ (no clear indication as to when /hc/ left, say it happened here)
Season 8, Episode 17 (Jan. 22, 2011) - /r9k/, /new/
Season 10, Episode 51 (Sep. 21, 2013) - /q/ (again)
Season 11, Episode 2 (Oct. 12, 2013) - /con/ (again)
Season 11, Episode 28 (Apr. 12, 2014) - /rs/
Season 11, Episode 33 (May 17, 2014) - /fk/ (episode opens, says he's leaving for college. /b/ is like "Who was that kid? Did /5/ come back?")
Season 12, Episode 31 (Apr. 30, 2016) - /film/ (lasts half the episode, leaves, finds that quests are much cooler)