Can warblades use strike maneuvers with improvised weapons? Would they be able to take the standard penalty for improvised weapons, or not be able to do so at all?
A martial adept that's using an improvised weapon initiates strikes normally
So far as I can tell, improvised weapons go unmentioned by Tome of Battle. That book's silence means the rules on improvised weapons from the Player's Handbook (113), Complete Warrior (158–9), and whatever other supplements the DM allows in the campaign apply normally.
This means that improvised weapons are just another kind of weapon for a martial adept. Of course, some strikes (and feats and special abilities) mandate the use of specific weapons, and an improvised weapon won't be of any use regarding those, but I'm pretty sure you knew that already.
Anyway, to be extra clear, Tome of Battle on Strikes, in part, says
A strike is a maneuver that allows a special attack.… Strikes almost always require a standard or full-round action to complete. Most of them involve a melee attack [n.b. not, for example, a simple, martial, or exotic melee weapon] as part of completing the maneuver. If the attack hits, your opponent typically takes normal melee damage, as well as suffering the effect of the strike. When making a strike, you use your base attack bonus, all attack and damage modifiers, weapon damage, and so forth, as normal.
You can make a critical hit with a strike, and in a few cases, a critical hit grants you additional benefits.… (42–3)
(Emphasis mine.) However, a typical warblade that wants to initiate a strike while employing an improvised weapon will suffer a −4 penalty due to nonproficiency on any attack rolls that the strike mandates. Eliminating that −4 penalty presents a significant challenge. (The ersatz Jackie Chan (no relation) may be interested in this answer that tries to eliminate that penalty.)
To save you asking more of these questions...
The sublime maneuvers from Tome of Battle do not care, at all, at any point, about what weapon you are using. They may care about the kind of attack you make, and some weapons may not be able to make that kind of attack, but the only thing the maneuvers care about is that the attack gets made. The weapon you use is irrelevant.
So it does not matter if you have proficiency, it does not matter if it’s a real weapon or improvised, it does not matter if you could also use that weapon to make another kind of attack: all that matters is that you make the kind of attack stated in the maneuver. There are no hidden gotchas.1 Tome of Battle simply does not care what weapon you use to initiate a maneuver.
That also means that the weapons associated with a given discipline are irrelevant to using maneuvers from that discipline. The only things that care what sort of weapon you use are a few of the feats, mostly the ones like Shadow Blade that are tied to a particular discipline and only work with the weapons associated with that discipline.
- Well, one, sort of: Stone Dragon maneuvers all must be initiated while standing on the ground. That has nothing to do with weapons, of course, but it is a surprising detail hidden away where you wouldn’t expect it, so “gotcha” applies. Of course, your game is better off ignoring that rule anyway, so if you missed it that’s fine.