If you've never seen these movies, they're some of the best, bloodiest samurai movies ever made and I cannot recommend them highly enough. According to reviews, there are some issues with picture quality at certain points, but everyone seems to agree that they're as good as is available. And the DVD box set is up close to $100, so they're also the most financially viable.
If you prefer your samurai bloodletting in English dub then
The Shogun Assassin films are basically the Lone Wolf & Cub films edited down to mostly just the violent parts and dubbed into English without much regard for the story. If you've seen Kill Bill Vol. 2, then you might remember that Shogun Assassin is the movie Uma Thurman's daughter wants to watch at bedtime.
Personally, I much prefer the original films in their original state, but if you're actually buying samurai films on Blu-ray, I support your decision.
And while I'm here, recommending samurai films that are currently cheap on eBay, you can also get The Hidden Blade for $11.
This is another great samurai movie, but it's a much slower film, more drama than action. I give it the highest possible recommendation, though. It's directed by Yoji Yamada (The Twilight Samurai, Love & Honor), so you can't go wrong.