Well, you can't perform Flurry of Blows or Stunning Fist with a katana (bastard sword). But you have many other options:

1) Be something else (Swordsage, Fighter, OA Samurai) entirely and call yourself a Monk. This is what I suggest doing.

2) Pick up a few levels of Monk for the bonus feats and then head into something else. I personally think that this is a cop out, since you're essentially doing the same thing as choice number 1. Wordmiser's suggetion is a solid one. Though I would throw in a few levels of Stalker of Kharash from Book of Exalted Deeds so that you can get Favored Enemy (Evil).

3) Use a really weird combo: Monk 6/Disciple of the Eye 5/Warmind 9
Pick up the PHBII Monk Flurry/Decisive Strike variant. You get fewer attacks, but each will deal double damage. Use unarmed attacks for all of these strikes (feet, elbows, headbutt, etc.)

Pick up the Karmic Strike feat (Comp Warrior, and eventually Robilar's Gambit from PHBII). Now whenever someone hits you in melee, you get a free attack of opportunity on them. Use your katana two handed. Thanks to Decisive Strike, each attack of opportunity deals double damage. AoO do not have the Monk Flurry weapon restrictions.

Disciple of the Eye will give you Fear attacks, which will cause enemies to run away (generating further double damage AoO). It also stacks to determine your Flurry/Decisive Strike ability.

War Mind will give you Sweeping Strike and access to Expansion, to improve your reach and damage.

Enjoy.