The UnitedSM Business Card has an outstanding offer to earn 75,000 bonus miles after you spend $5,000 on purchases in the first 3 months your account is open. That’s a lot of miles for a reasonable minimum spend requirement, and it’s exceptional value for a card with a $0 annual fee for the first year (then $99).
With a $0 first year annual fee you can even make money off of its $100 United travel credit offer, too, and the card even comes with club passes in the first year.