If you want ridiculous amounts of damage, look into the Iaijutsu Master PrC from Oriental Adventures. It's possible to make Iaijutsu Masters that can do thousands of points of damage in a round, if you max charisma and do things to make sure that your opponent is flat-footed a lot of the time. Have high Dex and Chr, and you'll beat everyone on initiative all the time. Use Flick of the Wrist from Song and Silence and a Sun Blade from the DMG in order to get them flat-footed if they manage to surprise you. You won't even need the levels in Master Samurai if you go this route, but they can't hurt I suppose. If you don't mind getting sneaky, take levels in Void Incarnate (can be found here:
http://www.wizards.com/default.asp?x=dnd/ei/20030418a ) once you get to epic levels, and every attack you make will catch your opponent flat-footed unless theyre a vermin or something.
The best part about the extra damage from Iaijutsu Focus is that it applies to uncrittable monsters, too, so you can do those thousands of damage to constructs, undead, something with concealment, something with fortified armor, etc., and it doesn't matter if they have their dex or not, just if they're flat-footed, so even Uncanny Dodge doesn't help against it (it allows them to retain their dex bonus to AC, but they are still considered flat-footed).
Anyway, if your DM allows it, and you don't mind using what is possibly one of the cheesiest melee PrCs in the game, this would be the way to go for an insane damage katana fighter.