For some reason, I've decided to go through every single spell in the Player's Handbook. Here's the first:
Bard - Cantrip - Blade Ward
Casting Time: 1 action
Components: V, S
Duration: 1 round
You extend your hand and trace a sigil of warding in the air. Until the end of your next turn, you have resistance against bludgeoning, piercing, and slashing damage dealt by weapon attacks.
My Comments: Sure, it's a cantrip so you can't expect much, but still, I can't say I'm impressed. Basically, you give up an action in one turn to reduce the damage you're going to take for ONE round.
Personally, I think you're probably better off using your action to do some damage.