I use American Express Plum. It's a trade terms card -- pay your bill within 10 days of the due date for a 1.5% discount on all your spending, or pay 10% of the bill and you have 60 days to pay the rest interest-free.

It's not a traditional credit card, you can't maintain a balance past 60 days... but there's also no credit limit. You can spend as much as your business needs. I've been given credit cards with useless spending limits; Amex let me charge over $10k in the first half month I had the card.

Amex has amazing customer service, and they'll FedEx 2-day the card to you and activate it on the phone with you as soon as you receive it. And you'll get all the benefits all Amex cards come with that almost no one else offers, from extended warranties on all purchases, accidental damage reimbursement, return protection to discounts on purchases at all the OPEN partners like OfficeMax, FedEx and hotels.