In my case I'm talking about Assassin's Stance, but I'd like to know the answer for stances in general. I feel like I might be missing something incredibly obvious caused by missing a word or two (or a paragraph), but I can't find anything that explicitly states whether or not I can use the Tome of Battle stances with ranged weapons like the bow (or crossbow). I realize that half the classes have "blade" in their names so using ranged weapons is not in the spirit of things, but I'm looking for an explicit answer (or as close to one as possible) from any WotC official resource. If this has already been answered I'm sorry, but I could not find the answer myself from searching.
Most things in Tome of Battle are specific to melee weapons, but nothing about maneuvers or stances in general is. Stances may be used with any weapon unless they specify melee-only—which many stances do.
For example, punishing stance says, in part,
you deal an extra 1d6 points of damage with all melee attacks.
so that is melee-only.
On the other hand, assassin’s stance only says that
you gain the sneak attack ability, which deals an extra 2d6 points of damage [...or] your existing sneak attack ability deals an extra 2d6 points of damage. See the rogue class feature (PH 50) for a complete description of sneak attack.
and sneak attack has this to say:
Ranged attacks can count as sneak attacks only if the target is within 30 feet.
So yes, with assassin’s stance you can add damage to your ranged attacks, provided that the target is within 30 feet and denied its Dexterity bonus to AC. Note that denying a creature’s Dexterity bonus can be non-trivial, and there is no way to take advantage of flanking with a ranged weapon, so assassin’s stance is definitely better in melee than it is at range.
For more on using Tome of Battle with a ranged character, some useful guides: