As far as the Zatoichi, my favorite is probaby "Zatoichi Meets the One Armed Swordsman". "Zatoichi Meets Yojimbo" is a close second because of Mifune and Katsu sharing the screen.
"The Hidden Fortress" is a really good adventure story (it is the basis for Star Wars) and the supporting cast is great. A good film for those who don't like the heavy drama of some Samurai films. Of course, the standard Kurosawa faire is always worth a watch ("Seven Samurai", "Rashomon", "Sanjuro", "Yojimbo", more recently "Ran")
"Samurai Assassin" has a really good snow battle as it's finale.
"Samurai Wolf 1 and 2" is good if you like Katsu's "Lone Wolf and Cub" series.
"Samurai Saga" is just beautiful to watch, but it is merely another adaptation of "Cyrano De Bergerac". Kind of like "Macbeth" and Kurosawa's, "Throne of Blood". Still worth watching for the beautiful cinematography. Mifune is excellent.
"Sword of Doom" and "The Betrayal" probably has the best choreographed swordplay of any Samurai films. Both are brutal and tragic.
"Bushido" is amazing in the fact that one actor played the seven roles of the main character's former generations as he reflects on his family's life throughout history.
Hope these recommendations are helpful!