Best intro offer
 

What are some miles cards with a good intro offer?

I've been looking at the United MileagePlus Explorer Business Card.

Any other cards with great intro offers?

There's a Sticky thread that tries to list those always at the top of this forum:
It's only updated to add newly-discovered offers (or deleted dead offers), so if you Subscribe to that thread, you can get an email every time a new offer is mentioned there.