Well, I played warblade many times and it's one of my favorite classes, sooo...
Diamond Mind and Iron Heart are definitely functional, but you need to know what to pick. In general, I recommend multiclassing and entering Warblade as late as possible. Also, try to write down character progress, noting which maneuvers on which levels will you take. There are requirements, which can make getting a maneuver impossible.
Overall, entering warblade late lets you get higher level maneuvers right away, which is important as there's no maneuver swapping implemented. So, if you enter warblade at 5, you have access to maneuvers of level 2. At level 9, level 3 maneuvers are available. Honestly, things at level 1 and 2 are useful, but nothing gamebreaking. Minotaur's Charge is nice. From the stances, Punishing Stance is worth looking at. Blood in the Water can be nice, but it's just a +1 to hit and damage. Stacking is not implemented (hard to code).
Level 3 maneuvers are a different story. Insightful Strike lets you hit for very nice damage. White Raven Tactics is broken in PnP, but doesn't seem to work in NWN (I didn't test it very thoroughly though). Iron Heart Surge is simply amazing, allowing you to shrug off ability damage, level drain and many other things. Others aren't that spectacular.
4th level maneuvers -> Mithral Tornado. Extremely useful when dealing with many foes. Also, I recommend Lightning Recovery, it's a free, addittional attack with a bonus to hit which does not cost you an action. Otherwise, Ruby Nightmare Blade is strong if you focus on slow, powerful hits. I don't really remember other schools
Level 5 is pretty forgettable, nothing really worth using IMO. Pick what you feel is best.
As for level 6, three awesome maneuvers here. My Wizard/Warblade/Jade Phoenix Mage abused the hell out of Iron Heart Endurance - healing twice your level every second round while beating on enemies was -very- strong. Greater Insightful Strike is twice as strong as the regular one, and there are ways to skyrocket your concentration roll. And last but not least - Moment of Alactrity. This maneuver acts as a one round time stop. It's a swift action, so you can attack during this round. Time stop your enemies every second turn? Hell yeah!
Level 7 is pretty forgettable again, but feel free to test the maneuvers. I might have missed something
Ah! Avalanche of Blades - test it out, especially, when you cast true strike before you use it (I believe there are items which have true strike on them).
Level 8 is all about Adamantine Hurricane. Two attacks against each enemy in range, at highest AB+4? Simply amazing. You can also try White Raven Hammer - repeatable stun is always welcome ( never used this maneuver though) and Diamond Nightmare Blade - the effect is awesome when you crit with a two-handed weapon and deal quadruple damage.
Level 9 - everything here is good, though I am not sure if War Master's Charge works.