Just sayin'
Too bad multiclassing & PrCls aren't allowed. If so, a Duskblade4/Favored Soul3/Kensai4 would be a pretty good front line Gishtank.
What each brings to the table:
1) Kensai4 has 4d10HD, +3 BAB, adds +4 worth of enhancements to his signature weapon, Ki Projection bonus of +2 to Bluff, Diplomacy, Gather Info & Intimidate and has a Power Surge giving him +8Str for 2 rounds, usable as many times in 24 hours as he can make the (increasingly difficult) Concentration check.
2) Duskblade4 gives 4d8HD, +4 BAB, Armored Mage (med), 0 & 1st lvl Arc spells, Combat Casting as a bonus feat, and Arcane Channeling (which, despite its name, allows the channelling of
any touch spell you know)
3) Favored Soul3 grants 3d8HD, +2BAB, Weapon Focus with the deity's favored weapon, and 0 & 1st lvl Div spells.
The PC gives up some HP, some AC and +2 BAB to the knight, but will have more skill points, greater situational flexibility (Kelgore's Fire Bolt is good, and if the PCs level up, Seeking Ray & Stretch Weapon are also quite nice), some healing, and makes up those lost BAB in the form of the Kensai's weapon enhancements and Power Surge.
In addition, taking the Smiting Spell Feat would let you channel a touch spell into a ranged weapon's ammo as well.
Flaws:
1) He'd need to take Combat Expertise as a prerequisite for Kensai, but since Duskblades are Int based casters, he'll easily meet the feat's requirement of a 13Int. However, Favored Souls need both Wis and Cha for spellcasting purposes. Combine all that with the stats for combat duties, and you're running a PC with MAD as bad as any PC ever had.
2) He only has enough spellpower to be a secondary caster at best, and most of that in direct melee combat or self-buffing of some kind. Since he's a front line tank, though, that's probably enough.
Some other thoughts:
Personally, I'm a big fan of DCv1, and expand the use of the book's Bloodline feats to all spontaneous arcane casters. That can broaden and deepen the power of either the Warmage or the Duskblade. It also has some nice combat (esp. polearm) feats and nifty weapons.
As far as the "Stealthy" or any other corner solution party build: only you as the DM know that for sure. Can all stealthy types avoid the direct challenges of the adventure and achieve the final goal? Can all warriors blast through the whole thing, or all spellcasters magic their way to success?
Also fun might be the Binder (Tome of Magic), the Spirit Shaman (Complete Divine), and all the Psionic classes.
I'd also add the Shadow Mage from ToM, or the 3 classes from the surprisingly good and definitely underappreciated Magic of Incarnum.
