Paladin in Citadel just posted a very true observation. Shields only give a 1 point bonus on your armor class in D&D. That's a 5% difference. But a real shield is much more effective than that. If you ever watched or joined an SCA rally, or tried your hand at swordfighting, you'll know what I mean.
For me it was a main reason to switch game systems to "something more realistic", like RuneQuest (this was in 1983 or something). The other reason was wanting to use spell points instead of memorizing spells.
A shield is very effective to hide behind when being shot at, and it's almost as effective when being hacked at. When many shields are combined into a "shield wall", with each soldier next to the other overlapping shields, it's much like a tank coming at you. Shields are much more than a +1 on AC.
So, unless you also want to switch systems (to my Dark Dungeon 2nd ed for example, hint hint), you might want to try this D&D hack instead.
Shields need one free hand to use, and give a +1 on your armor class. But...
You can also use them to go "on the defensive". Then you really hide behind your shield, and forfeit some of your chances to attack. The effects are then according to this table.
buckler: too small for this tactic, just a +1 on AC
normal shield: +3 on defense, -3 on own attack in same round
large shield: +5 on defense, -5 on own attack in same round
Note that the defensive tactic is especially handy when used against missile fire (where you don't couterattack anyway), and for higher level characters with better attack skill.
The extra defense value of the shield is in a single direction only, or two hexsides if you use hexes.
Shields can be hacked to pieces if hit by heavier weapons (when the hit would normally be enough to hit AC 9). A normal shield should have about 5 hits, a large one 7, reinforced shields one or two points better.
I'd use a shield if I'd play a fighter with these extra rules. See what your players do. See what the sentient monsters and NPCs do... like an orc with a shield. What a way to introduce that rule, with a horde of orcs with large shields :-)