I'm a bit leery of my shield feats--they're good and powerful feats mechanically, but whether players would have much fun with that PC.
"Attack me! Leave my friend alone and take my Hit Points instead!" is not something players often say.
But I just found something in the SRD Variant rules that would make the Defender-type fighter a more fun roleplay. Roughly, reduce the AC bonus of armor by 1/2, and gain 1/2 the value in DR.
Now, Mr Fighter with Fullplate & Shield with BAW-Shield at 10th level (and no magic just to make the math easier) is rolling at AC 21 (10 + 2 shield + 4 Full plate + 5 1/2 BAB) and DR 4. Mr Cleric (Full Plate, Shield, Mace) is at AC 16, DR 4. So it makes a little more sense for Mr Fullplate to jump in front of the arrow or greataxe or claw aimed at Mr Wizard if Mr Fullplate knows he's got a little bit of Damage Reduction.