Big fan here! I love Vagabond's stunning drawing style and fun characterization of historical figures. The visualizations of sword fights are the best I've seen.
A few other martial-arts /action ones:
子連れ狼 Kozure Ōkami / Lone Wolf and Cub
A canonical manga. Lots of sword-fighting and bushido references.
半蔵の門 Hanzō no Mon / Hanzo's Gate / Path of the Assassin
Same authors as Lone Wolf and Cub. Interesting and fun take on ninjutsu and Tokugawa history.
シグルイ Shigurui / Death Frenzy
The most disturbing manga I've seen. Shows the "ugly" side of one brutal koryu. There's also an anime version that is a work of visual art. Don't try the "nagare boshi" technique lol