Zatoichi is a great series. I have not read the manga yet, but the movie series was awesome. Blade of the Immortal is another one I agree with. Great movie adapation as well.
Another manga that got a great movie series adaptation of is Lone Wolf and Cub. One of my all time favorites. It gets really deep into Bushido. So deep that I often had to reread chapters a few times in order to grasp what happened, and why. He explains a lot of the subtleties of it, very well. As well as a lot of feudal Japanese life and politics. Truly a great read.
Rurouni Kenshin is a good one, if you are looking for a lighter take on the genre. Though the original OVA was heavy AF, with less of the lightheartedness. Blew me away when I first saw it actually.
Or if you want fantasy, there is always Tenchi Muyo! Lots of sword fighting in that one. The original series is still one of the all time greatest animes ever.
Ninja Scroll is another classic. Both of them were good.