Grappler build recommendation
Human. Monk for two levels, switch alignment to Neutral or Chaotic, then Barbarian 1 and fighter the rest of the way. This gives you Improved Grapple and unarmed strike, rage and Greater Weapon Specialization (Armor Spikes). Put stats in Str, Con.
Wear spiked light armor (mithral breastplate). Add Holy, Frost, Flaming, Shocking to your +1 adamantine armor spikes for extra damage. With light armor, you lose a couple of minor Monk abilities (Flurry, Wis bonus to AC), but you retain Barbarian fast movement.
Take Power Attack, Improved Toughness and Extra Rage feats. Ignore Reaping Mauler, Close Quarters Fighting, and all of those other Complete Warrior things. Take the Mage Slayer feat from Complete Arcane.
The 3.5e PH says armor spikes inflict extra piercing damage after a successful grapple check. This might mean you get your Str bonus to damage twice (once on unarmed strike damage, again on armor spikes). The 3.5e FAQ kind of makes that rule revert to the 3e version of armor spikes, but that FAQ entry may mean that you have the option of NOT inflicting extra damage if you don't want to. Ask your DM.
Power Attack adds to your unarmed strike damage, but may not (at DM's option; rules are ambiguous) decrease your grapple check. Grapple damage is like unarmed strike. But Power Attack doesn't give a damage bonus to armor spikes (they're a light martial weapon).
Carry a decent greatsword (+1 adamantine Ghost Touch) and a +1 Holy bow for those foes who can't be grappled. Boots of Speed. Some means of flying. Belt of Giant Strength. Amulet of Health. Gloves of Fearsome Grip (A&EG, +5 grapple checks). Cloak of Displacement. Vest of Resistance. Ring of Spell Storing (Enlarge Person, Alter Self, True Strike, Silence, Mirror Image) (might want to carry scrolls to help your caster buddies to recharge your ring). Ring of Counterspells (Dominate Person).
If your caster buddies usually lead off with Haste, change Boots of Speed to Winged Boots.
The Greater Magic Weapon spell is your friend, especially if your caster buddy has the Chain Spell feat.
With Silence from your bard or cleric buddy or from your Ring of Spell Storing, you grapple an enemy spellcaster and he's toast. Pin him to make sure or just squish him.
Rely on Displacement and Mirror Image instead of armor class, or just rely on big HP cuz yer gonna get hit anyway.