Really, Iron Guard's Glare and Shield Block with a heavy or tower shield (or a spell that gives a shield bonus to AC, for that matter) is a really solid tanking combo. Assuming the enemy's to-hit doesn't completely outclass the party's AC (and that's on your GM) and decent reach, you can easily give opponents a -4 to -12 (or -20% to -60% chance) to hit allies. Rapidly your GM (and through him, the monsters) will learn that to hit anything he will have to attack you. I have been running a campaign from 5th level up to 8th now, and so far the party Crusader has been very effective at "taking aggro" in this manner. Note that enemies are aware of the effects of iron guard's glare, and they will become immediately aware of the potency of shield block the first time you use it in combat. Both of these need only one level of Crusader to take, as either your 5th or 9th level (or so I recommend).
I second Dictum Mortuum's idea for divine Abjurant Champion (if it is acceptable to your GM) coupled with Divine Magician, which would allow you to add 9 wizard spells to your cleric spell list, notably shield. Note that shield block can be used with spell shields, so that would give +13 AC to adjacent allies with 5 levels of Abjurant Champion. I recently made a build that did this and used Shield Specialization(Spell) and Shield ward to get the +10 shield bonus to a slew of things, but mostly touch AC. If using shield specialization for spells is too cheesy for you or you want to cut down on feats, Parrying Shield is a great alternative (Shield to Touch AC only, but only 1 feat). For armor you would cast luminous armor or the greater version, of course. This allows you to have high dex as well, to fuel combat reflexes and thus lock-down.
When combining Tome of Battle with other classes without using the ToB PRCs, I would always recommend only dipping 1 or 2 levels of your initiator class. The thing about ToB is that it is amazingly friendly to dipping, in a way no other classes are really. A Cleric 18/Crusader 2 is maneuvers-wise competitive with an 10-11th level character. A Crusader 18/Cleric 2 is spell-wise equivalent to a second level character.
Another note about the role of healer: what many people overlook is that in D&D, "Healing" is not strictly, and even not often, a matter of hit point restoration. The party can deal with HP loss: through magic items such as wands and potions, class abilities, feats, maneuvers, and even good old fashion bed rest. Even arcane casters and psionic characters get a limited array of hit point healing spells. In my mind, a true healer in D&D is able to handle the more potent afflictions that characters aren't able to cure readily on their own: Negative levels, Ability Damage/Drain, Petrification, other long duration or permanent crowd control, and the big one: Death. Often times, you wont even GET a chance to heal a character before he dies: some trap will trigger, some group of monsters will get a lucky string of rolls, or a spellcaster will nuke the party with high damage or save or dies. And at that point you will realize that what a Crusader grants is not healing exactly but sustainability, and there is a big difference. I'm not saying Crusader is bad (in fact I love the class) but their capstone healing ability is Heal, not True Resurrection.
