Hmm...Well Rurouni Kenshin/Samurai X started it all for me so I have to recommend that. But if you are looking for a shounen anime I recommend Samurai Champloo.
Not that RK isn't considered shounen but it is highly romanticized by its shoujo fans.
Samurai Champloo has some great animated fight scenes, it doesn't sugar coat anything, it can be gritty and even though the 2 main male characters could be considered attractive by some, the anime isn't loaded with bishies so there is nothing distracting you from what you are watching if you get me.