Okay, I have a ton of episodes, so this is a long list...
Episode #0001 (OAD: 06/27/1966) - I just love watching this episode. It's so well-crafted and well-written, and you can tell a bit more effort went into this episode than any of the ones that followed.
Episodes #0126 & #0127 (OAD: 12/19-20/1966) - Victoria is rescused from Matthew by the ghosts of Josette and Bill Malloy. GhostJosette floats around the columns of the Old House. Really good conclusion to the murderous Matthew storyline.
Episode #0191 (OAD: 03/20/1967) - After getting a message from Josette, Victoria goes to the fishing shack to save David from Laura. Elizabeth comes out of her coma. An outstanding conclusion to an outstanding story.
Episode #0210 (OAD: 04/17/1967) - Episode prior to the first appearance of Barnabas. Willie goes to the family crypt and unleashes a monster.
Episode #0271 (OAD: 07/10/1967) - Elizabeth confesses to Paul's murder after she ends the wedding.
Episodes #0280 & 281 (OAD: 07/21/1967 & 07/24/1967) - The big costume party at the Old House. I simply adore these episodes.
Episode #0366 (OAD: 11/20/1967) - Victoria finds herself in 1795.
Episode #0405 (OAD: 01/12/1967) - Angelique curses Barnabas.
Episode #0461 (OAD: 04/01/1968) - Victoria returns to the present after being hung as a witch in 1795.
Episode #0657 (OAD: 12/31/1968) - Victoria's ghost begins to haunt Collinwood.
Episode #0691 (OAD: 02/17/1969) - Elizabeth and Mrs. Johnson finally realize that Amy and David have become posessed.
Episode #0693 (OAD: 02/19/1969) - A failed exorcism is performed on Collinwood.
Episode #0694 (OAD: 02/20/1969) - The Collins family is forced to flee Collinwood.
Episode #0711 (OAD: 03/17/1969) - Angelique is summoned to 1897 by Quentin and Evan.
Episode #0746 (OAD: 05/05/1969) - Magda and Jenny reunite. I'm not sure about this one, but it's the one episode that came to mind. I just loved all the episodse with Jenny.
Episodes #0803 & #804 (OAD: 07/23-24/1969) - Due to Petofi's posession of Jamison, Edward thinks he is a servant while Charity is convinced she is Pansy Faye.
Really enjoyed 1897, but I had trouble coming up with specific episodes from that period of the show. Again, I really liked the Jenny storyline and the beginning of the Kitty storyline.
Episode #1001 (OAD: 04/27/1970) - Angelique and Alexis switch places.
Episode #1049 (OAD: 07/02/1970) - Carolyn is killed by the serial killer.
Episode #1053 (OAD: 07/08/1970) - The identity of the serial killer is revealed when Elizabeth confronts him.
Episodes #1061-1070 (OAD: 07/20-31/1970) - Barnabas and Julia travel to 1995. Really enjoyed this short arc and can't come up with one particular episode.
Episode #1109 (OAD: 09/24/1970) - Zombies destroy Collinwood.
OK, I really, really love 1840, but again, I'm having trouble thinking of episodes from it. I truly enjoyed most of the storylines, especially anything dealing with Samantha.
Episode #1197 (OAD: 01/26/1971) - Quentin and Desmond are saved; Gerard dies. Barnabas tells Angelique he loves her; Angelique dies.
Episode #1231 (OAD: 03/15/1971) - The events of 1680 are revealed.
Episode #1237 (OAD: 03/23/1971) - Gabriel dies. Kendrick begins to reveal Melanie's maternity.
Episode #1238 (OAD: 03/24/1971) - Daphne dies. Melanie finds out who her real mother is and is very, very happy.
Episode #1245 (OAD: 04/02/1971) - The final episode.