Well, there are a few good shields out there that you might want to check out:
Spellbreaker - creates a ward that protects against spells, up to a limit;
Targe of the Blooded - it causes a light bleed effect when shield bashing;
Shield of Ysgramor - one of my favorite shields; it increases your magic resist by 20%, and it stacks nicely with the perk Elemental Protection, and it increases health;
Shield of Solitude - even better than the Shield of Ysgramor; increases magic resist by 30% and blocks 35% more damage
Later on, once you can enchant an item with 2 enchantments, you could make your shield block more damage and increase magic resist. In my mind, that's pretty much the best enchantments you can add to them, plus the fact that you get Elemental Protection and, of course, Shield Charge.